Loans Held-for-Investment (Allowance for Loan Losses) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Jun. 30, 2016
Dec. 31, 2015
Dec. 31, 2014
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses $ 162   $ 222 $ 253 $ 297       $ 207       $ 305 $ 187 $ 297 $ 297 $ 207 $ 305      
Charge-offs (10)     (21)                   (24) (64) (101) (52) (197)      
Recoveries 1     3                   3 6 10 10 29      
Provision (3) $ (1) (1) (13) (4) $ 5 $ 8 $ 6 112 $ 14 $ 4 $ 31 21 (16) (17) (19) 132 70      
Ending balance allowance for loan losses 150 187   222 253 297       207       150 222 187 297 207      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     $ 77 $ 120 $ 417
Loans held-for-investment, collectively evaluated                                     5,657 6,121 3,820
Total loans                                     5,734 6,241 4,237
Allowance for loan losses, individually evaluated                                     16 20 88
Allowance for loan losses, collectively evaluated                                     134 167 209
Total allowance for loan losses 162 187 222 253 297 297     207 207     305 187 297 297 207 305 150 187 297
Financing Receivable, Significant Sales       15                     51            
Residential first mortgage                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 95   151 188 234       162       220 116 234 234 162 220      
Charge-offs (8)     (19)                   (19) (60) (87) (38) (133)      
Recoveries 1     1                   1 2 3 3 15      
Provision (7)     (19)                   (17) (25) (34) 107 60      
Ending balance allowance for loan losses 81 116   151 188 234       162       81 151 116 234 162      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     43 87 385
Loans held-for-investment, collectively evaluated                                     2,027 3,007 1,782
Total loans                                     2,070 3,094 2,167
Allowance for loan losses, individually evaluated                                     7 12 82
Allowance for loan losses, collectively evaluated                                     74 104 152
Total allowance for loan losses 95 116 151 188 234 234     162 162     220 116 234 234 162 220 81 116 234
Second mortgage                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 10   14 12 12       12       20 11 12 12 12 20      
Charge-offs (1)     (1)                   (2) (2) (4) (3) (6)      
Recoveries 1     1                   1 1 2 1 1      
Provision 0     2                   0 3 1 2 (3)      
Ending balance allowance for loan losses 10 11   14 12 12       12       10 14 11 12 12      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     27 28 31
Loans held-for-investment, collectively evaluated                                     61 65 65
Total loans                                     88 93 96
Allowance for loan losses, individually evaluated                                     6 6 5
Allowance for loan losses, collectively evaluated                                     4 5 7
Total allowance for loan losses 10 11 14 12 12 12     12 12     20 11 12 12 12 20 10 11 12
HELOC                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 20   25 21 19       8       18 21 19 19 8 18      
Charge-offs 0     0                   (1) (1) (3) (6) (5)      
Recoveries (1)     0                   0 0 0 0 1      
Provision 1     4                   0 7 5 17 (6)      
Ending balance allowance for loan losses 20 21   25 21 19       8       20 25 21 19 8      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     6 3 1
Loans held-for-investment, collectively evaluated                                     296 318 124
Total loans                                     302 321 125
Allowance for loan losses, individually evaluated                                     3 1 1
Allowance for loan losses, collectively evaluated                                     17 20 18
Total allowance for loan losses 20 21 25 21 19 19     8 8     18 21 19 19 8 18 20 21 19
Other                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 2   1 0 1       2       2 2 1 1 2 2      
Charge-offs (1)     (1)                   (2) (1) (4) (2) (4)      
Recoveries 0     1                   1 1 3 3 2      
Provision 0     1                   0 0 2 (2) 2      
Ending balance allowance for loan losses 1 2   1 0 1       2       1 1 2 1 2      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     0 0 0
Loans held-for-investment, collectively evaluated                                     32 31 31
Total loans                                     32 31 31
Allowance for loan losses, individually evaluated                                     0 1 0
Allowance for loan losses, collectively evaluated                                     1 1 1
Total allowance for loan losses 2 2 1 0 1 1     2 2     2 2 1 1 2 2 1 2 1
Commercial real estate                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 19   15 16 17       19       41 18 17 17 19 41      
Charge-offs 0     0                   0 0 0 (3) (47)      
Recoveries 0     0                   0 2 2 3 10      
Provision 0     (1)                   1 (4) (1) (2) 15      
Ending balance allowance for loan losses 19 18   15 16 17       19       19 15 18 17 19      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     0 0 0
Loans held-for-investment, collectively evaluated                                     976 814 620
Total loans                                     976 814 620
Allowance for loan losses, individually evaluated                                     0 0 0
Allowance for loan losses, collectively evaluated                                     19 18 17
Total allowance for loan losses 19 18 15 16 17 17     19 19     41 18 17 17 19 41 19 18 17
Commercial and industrial                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 10   12 12 11       3       3 13 11 11 3 3      
Charge-offs 0     0                   0 0 (3) 0 (2)      
Recoveries 0     0                   0 0 0 0 0      
Provision 1     0                   (2) 1 5 8 2      
Ending balance allowance for loan losses 11 13   12 12 11       3       11 12 13 11 3      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     1 2 0
Loans held-for-investment, collectively evaluated                                     614 550 429
Total loans                                     615 552 429
Allowance for loan losses, individually evaluated                                     0 0 0
Allowance for loan losses, collectively evaluated                                     11 13 11
Total allowance for loan losses 10 13 12 12 11 11     3 3     3 13 11 11 3 3 11 13 11
Warehouse lending                                          
Allowance for Loan Losses [Roll Forward]                                          
Beginning balance allowance for loan losses 6   4 4 3       1       1 6 3 3 1 1      
Charge-offs 0     0                   0 0 0 0 0      
Recoveries 0     0                   0 0 0 0 0      
Provision 2     0                   2 1 3 2 0      
Ending balance allowance for loan losses 8 6   4 4 3       1       8 4 6 3 1      
Allowance for Loan Losses, Additional Disclosure [Abstract]                                          
Loans held-for-investment, individually evaluated                                     0 0 0
Loans held-for-investment, collectively evaluated                                     1,651 1,336 769
Total loans                                     1,651 1,336 769
Allowance for loan losses, individually evaluated                                     0 0 0
Allowance for loan losses, collectively evaluated                                     8 6 3
Total allowance for loan losses $ 6 $ 6 $ 4 $ 4 $ 3 $ 3     $ 1 $ 1     $ 1 $ 6 $ 3 $ 3 $ 1 $ 1 $ 8 $ 6 $ 3