Loans Held-for-Investment (Impaired Loans) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Financing Receivable, Impaired [Line Items]              
With no related allowance recorded, recorded investment $ 3   $ 3   $ 25 $ 64  
With no related allowance recorded, unpaid principal balance 3   3   22 85  
With an allowance recorded, recorded investment 73   73   96 351  
With an allowance recorded, unpaid principal balance 74   74   98 356  
With an allowance recorded, related allowance 16   16   20 89  
Total recorded investment 76   76   121 415  
Total unpaid principal balance 77   77   120 441  
Average Recorded Investment 80 $ 149 95 $ 243 191 432 $ 673
Interest Income Recognized 1 1 2 3 5 12 19
Residential first mortgage              
Financing Receivable, Impaired [Line Items]              
With no related allowance recorded, recorded investment 2   2   20 63  
With no related allowance recorded, unpaid principal balance 2   2   20 78  
With an allowance recorded, recorded investment 41   41   65 321  
With an allowance recorded, unpaid principal balance 41   41   67 326  
With an allowance recorded, related allowance 6   6   12 82  
Total recorded investment 43   43   85 384  
Total unpaid principal balance 43   43   87 404  
Average Recorded Investment 47 116 60 210 150 402 603
Interest Income Recognized 0 1 1 2 5 11 17
Second mortgage              
Financing Receivable, Impaired [Line Items]              
With no related allowance recorded, recorded investment         0 1  
With no related allowance recorded, unpaid principal balance         0 6  
With an allowance recorded, recorded investment 26   26   28 29  
With an allowance recorded, unpaid principal balance 27   27   28 29  
With an allowance recorded, related allowance 7   7   6 6  
Total recorded investment 26   26   28 30  
Total unpaid principal balance 27   27   28 35  
Average Recorded Investment 27 31 27 31 29 28 21
Interest Income Recognized 1 0 1 1 0 1 1
HELOC              
Financing Receivable, Impaired [Line Items]              
With no related allowance recorded, recorded investment         0 0  
With no related allowance recorded, unpaid principal balance         0 1  
With an allowance recorded, recorded investment 6   6   3 1  
With an allowance recorded, unpaid principal balance 6   6   3 1  
With an allowance recorded, related allowance 3   3   1 1  
Total recorded investment 6   6   3 1  
Total unpaid principal balance 6   6   3 2  
Average Recorded Investment 5 2 5 2 10 1 1
Interest Income Recognized 0 0 0 0 0 0 0
Total consumer loans              
Financing Receivable, Impaired [Line Items]              
With an allowance recorded, recorded investment         0 0  
With an allowance recorded, unpaid principal balance         0 0  
With an allowance recorded, related allowance         1 0  
Total recorded investment         0 0  
Total unpaid principal balance         0 0  
Commercial and industrial              
Financing Receivable, Impaired [Line Items]              
With no related allowance recorded, recorded investment 1   1   5 0  
With no related allowance recorded, unpaid principal balance 1   1   2 0  
With an allowance recorded, related allowance 0   0   0 0  
Total recorded investment 1   1   5 0  
Total unpaid principal balance 1   1   2 0  
Average Recorded Investment 1 0 3 0 2 0 2
Interest Income Recognized 0 $ 0 0 $ 0 0 0 0
Commercial real estate              
Financing Receivable, Impaired [Line Items]              
Average Recorded Investment         0 1 46
Interest Income Recognized         0 $ 0 $ 1
Other Consumer and Commercial Loans              
Financing Receivable, Impaired [Line Items]              
With an allowance recorded, recorded investment 0   0   0    
With an allowance recorded, unpaid principal balance 0   0   0    
With an allowance recorded, related allowance 0   0   1    
Total recorded investment 0   0   0    
Total unpaid principal balance $ 0   $ 0   $ 0