Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale $ 1,145,000,000   $ 1,294,000,000 $ 1,672,000,000  
Loans held-for-sale 3,071,000,000   2,541,000,000 1,196,000,000  
Loans held-for-investment 88,000,000   111,000,000 211,000,000  
Mortgage servicing rights 301,000,000   296,000,000 258,000,000  
Total assets at fair value 3,159,000,000   2,652,000,000 1,407,000,000 $ 1,379,000,000
Liabilities, Fair Value Disclosure [Abstract]          
Long-term Debt, Fair Value     0 84,000,000  
Agency - Commercial          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 640,000,000   766,000,000 540,000,000  
Agency - Residential          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 473,000,000   514,000,000 1,130,000,000  
Municipal obligations          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 32,000,000   14,000,000 2,000,000  
Level 2          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 1,145,000,000        
Recurring          
Liabilities, Fair Value Disclosure [Abstract]          
Fair Value, Assets and Liabilities, Transfers Between Fair Value Levels 0 $ 0      
Recurring | Level 1          
Assets, Fair Value Disclosure [Abstract]          
Mortgage servicing rights 0   0 0  
Derivative assets 3,000,000   0 9,000,000  
Other Investments, Fair Value Disclosure       0  
Total assets at fair value 3,000,000   0 9,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities (3,000,000)   (1,000,000) (1,000,000)  
Warrant liabilities 0   0 0  
Long-term Debt, Fair Value       0  
DOJ litigation settlement 0   0 0  
Total liabilities at fair value (3,000,000)   (1,000,000) (1,000,000)  
Recurring | Level 1 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 0  
Recurring | Level 1 | Mortgage backed securities forwards          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 2,000,000  
Recurring | Level 1 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 1 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       7,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (1,000,000) (1,000,000)  
Recurring | Level 1 | Forward agency and loan sales          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 1 | Interest rate swaps on FHLB advances          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0    
Recurring | Level 1 | Residential first mortgage loans          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-sale 0   0 0  
Loans held-for-investment 0   0 0  
Recurring | Level 1 | Second mortgage          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 0   0 0  
Recurring | Level 1 | Agency - Commercial          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Recurring | Level 1 | Agency - Residential          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Recurring | Level 1 | Municipal obligations          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Recurring | Level 1 | HELOC          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 0   0 0  
Recurring | Level 2          
Assets, Fair Value Disclosure [Abstract]          
Mortgage servicing rights 0   0 0  
Derivative assets 92,000,000   32,000,000 6,000,000  
Other Investments, Fair Value Disclosure       0  
Total assets at fair value 4,314,000,000   3,873,000,000 2,898,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities (130,000,000)   (17,000,000) (19,000,000)  
Warrant liabilities (9,000,000)   (8,000,000) (6,000,000)  
Long-term Debt, Fair Value       0  
DOJ litigation settlement 0   0 0  
Total liabilities at fair value (139,000,000)   (25,000,000) (25,000,000)  
Recurring | Level 2 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 0  
Recurring | Level 2 | Mortgage backed securities forwards          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     7,000,000 0  
Recurring | Level 2 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     25,000,000 6,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (7,000,000) (6,000,000)  
Recurring | Level 2 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 2 | Forward agency and loan sales          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (6,000,000) (13,000,000)  
Recurring | Level 2 | Interest rate swaps on FHLB advances          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (4,000,000)    
Recurring | Level 2 | Residential first mortgage loans          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-sale 3,071,000,000   2,541,000,000 1,196,000,000  
Loans held-for-investment 6,000,000   6,000,000 26,000,000  
Recurring | Level 2 | Second mortgage          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 0   0 0  
Recurring | Level 2 | Agency - Commercial          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 640,000,000   766,000,000 540,000,000  
Recurring | Level 2 | Agency - Residential          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 473,000,000   514,000,000 1,130,000,000  
Recurring | Level 2 | Municipal obligations          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 32,000,000   14,000,000 0  
Recurring | Level 2 | HELOC          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 0   0 0  
Recurring | Level 3          
Assets, Fair Value Disclosure [Abstract]          
Mortgage servicing rights 301,000,000   296,000,000 258,000,000  
Derivative assets 83,000,000   26,000,000 31,000,000  
Other Investments, Fair Value Disclosure       100,000,000  
Total assets at fair value 466,000,000   428,000,000 576,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities 0   0 0  
Warrant liabilities 0   0 0  
Long-term Debt, Fair Value       84,000,000  
DOJ litigation settlement (84,000,000)   (84,000,000) (82,000,000)  
Total liabilities at fair value (84,000,000)   (84,000,000) (166,000,000)  
Transfers between fair value levels     0 4,000,000 $ 0
Recurring | Level 3 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     26,000,000 31,000,000  
Recurring | Level 3 | Mortgage backed securities forwards          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 0  
Recurring | Level 3 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     0 0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 3 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 3 | Forward agency and loan sales          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0 0  
Recurring | Level 3 | Interest rate swaps on FHLB advances          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     0    
Recurring | Level 3 | Residential first mortgage loans          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-sale 0   0 0  
Loans held-for-investment 0   0 0  
Recurring | Level 3 | Second mortgage          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 38,000,000   42,000,000 53,000,000  
Recurring | Level 3 | Agency - Commercial          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Recurring | Level 3 | Agency - Residential          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Recurring | Level 3 | Municipal obligations          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 2,000,000  
Recurring | Level 3 | HELOC          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 44,000,000   64,000,000 132,000,000  
Total fair value          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 1,145,000,000   1,294,000,000 1,672,000,000  
Loans held-for-sale 3,094,000,000   2,578,000,000 1,196,000,000  
Loans held-for-investment 5,640,000,000   6,121,000,000 3,998,000,000  
Mortgage servicing rights 301,000,000   296,000,000 258,000,000  
Other Investments, Fair Value Disclosure       100,000,000  
Other Assets, Fair Value Disclosure 178,000,000   210,000,000    
Derivative Asset, Fair Value, Gross Asset 178,000,000   58,000,000    
Liabilities, Fair Value Disclosure [Abstract]          
Warrant liabilities (9,000,000)   (8,000,000)    
Long-term Debt, Fair Value 77,000,000   89,000,000 172,000,000  
Total fair value | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       31,000,000  
Total fair value | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       6,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       (6,000,000)  
Total fair value | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       7,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       (1,000,000)  
Total fair value | Level 1          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 0  
Loans held-for-sale 0   0 0  
Loans held-for-investment 0   0 0  
Mortgage servicing rights 0   0 0  
Other Investments, Fair Value Disclosure       0  
Other Assets, Fair Value Disclosure 0   0    
Derivative Asset, Fair Value, Gross Asset 3,000,000   0    
Liabilities, Fair Value Disclosure [Abstract]          
Warrant liabilities 0   0    
Long-term Debt, Fair Value 0   0 0  
Total fair value | Level 1 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Total fair value | Level 1 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       0  
Total fair value | Level 1 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       7,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       (1,000,000)  
Total fair value | Level 2          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale     1,294,000,000 1,670,000,000  
Loans held-for-sale 3,094,000,000   2,578,000,000 1,196,000,000  
Loans held-for-investment 6,000,000   6,000,000 26,000,000  
Mortgage servicing rights 0   0 0  
Other Investments, Fair Value Disclosure       0  
Other Assets, Fair Value Disclosure 178,000,000   210,000,000    
Derivative Asset, Fair Value, Gross Asset 92,000,000   32,000,000    
Liabilities, Fair Value Disclosure [Abstract]          
Warrant liabilities (9,000,000)   (8,000,000)    
Long-term Debt, Fair Value 77,000,000   89,000,000 88,000,000  
Total fair value | Level 2 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Total fair value | Level 2 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       6,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       (6,000,000)  
Total fair value | Level 2 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       0  
Total fair value | Level 3          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 0   0 2,000,000  
Loans held-for-sale 0   0 0  
Loans held-for-investment 5,634,000,000   6,115,000,000 3,972,000,000  
Mortgage servicing rights 301,000,000   296,000,000 258,000,000  
Other Investments, Fair Value Disclosure       100,000,000  
Other Assets, Fair Value Disclosure 0   0    
Derivative Asset, Fair Value, Gross Asset 83,000,000   26,000,000    
Liabilities, Fair Value Disclosure [Abstract]          
Warrant liabilities 0   0    
Long-term Debt, Fair Value 0   0 84,000,000  
Total fair value | Level 3 | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       31,000,000  
Total fair value | Level 3 | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       0  
Total fair value | Level 3 | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       0  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities       0  
Total fair value | Recurring          
Assets, Fair Value Disclosure [Abstract]          
Mortgage servicing rights 301,000,000   296,000,000 258,000,000  
Derivative assets 178,000,000   58,000,000 46,000,000  
Other Investments, Fair Value Disclosure       100,000,000  
Total assets at fair value 4,783,000,000   4,301,000,000 3,483,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities (133,000,000)   (18,000,000) (20,000,000)  
Warrant liabilities (9,000,000)   (8,000,000) (6,000,000)  
Long-term Debt, Fair Value       84,000,000  
DOJ litigation settlement (84,000,000)   (84,000,000) (82,000,000)  
Total liabilities at fair value (226,000,000)   (110,000,000) (192,000,000)  
Total fair value | Recurring | Rate lock commitments          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     26,000,000 31,000,000  
Total fair value | Recurring | Mortgage backed securities forwards          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     7,000,000 2,000,000  
Total fair value | Recurring | Interest rate swaps and swaptions          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets     25,000,000 6,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (7,000,000) (6,000,000)  
Total fair value | Recurring | U.S. Treasury and euro dollar futures          
Assets, Fair Value Disclosure [Abstract]          
Derivative assets       7,000,000  
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (1,000,000) (1,000,000)  
Total fair value | Recurring | Forward agency and loan sales          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (6,000,000) (13,000,000)  
Total fair value | Recurring | Interest rate swaps on FHLB advances          
Liabilities, Fair Value Disclosure [Abstract]          
Derivative liabilities     (4,000,000)    
Total fair value | Recurring | Residential first mortgage loans          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-sale 3,071,000,000   2,541,000,000 1,196,000,000  
Loans held-for-investment 6,000,000   6,000,000 26,000,000  
Total fair value | Recurring | Second mortgage          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment 38,000,000   42,000,000 53,000,000  
Total fair value | Recurring | Agency - Commercial          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 640,000,000   766,000,000 540,000,000  
Total fair value | Recurring | Agency - Residential          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 473,000,000   514,000,000 1,130,000,000  
Total fair value | Recurring | Municipal obligations          
Assets, Fair Value Disclosure [Abstract]          
Investment securities available-for-sale 32,000,000   14,000,000 2,000,000  
Total fair value | Recurring | HELOC          
Assets, Fair Value Disclosure [Abstract]          
Loans held-for-investment $ 44,000,000   $ 64,000,000 $ 132,000,000