Quarterly Financial Data (Unaudited) (Details) - USD ($)
$ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]                                    
Interest income $ 99 $ 95 $ 91 $ 90 $ 79 $ 72 $ 75 $ 72 $ 66 $ 72 $ 79 $ 85 $ 95 $ 200 $ 169 $ 355 $ 286 $ 330
Interest expense 22 19 18 17 14 11 11 9 8 31 36 38 39 44 31 68 39 144
Net interest income 77 76 73 73 65 61 64 63 58 41 43 47 56 156 138 287 247 186
(Benefit) provision for loan losses (3) (1) (1) (13) (4) 5 8 6 112 14 4 31 21 (16) (17) (19) 132 70
Net interest income after provision for loan losses 80 77 74 86 69 56 56 57 (54) 27 39 16 35 172 155 306 115 116
Net gain on loan sales 90 46 68 83 91 53 52 55 45 45 75 144 137 165 174 288 206 402
Loan fees and charges 19 14 17 19 17                 34 36 67 73 104
Loan administration income 4 7 8 7 4 5 6 6 7 3 1 1 1 10 11 26 24 6
Net (loss) return on the mortgage servicing assets (4) 9 12 9 (2) 2 1 5 16 17 27 31 15 (10) 7      
Representation and warranty benefit 4 6 6 5 2 6 (13) (5) 2 15 (5) (29) (17) 6 7 19 (10) (36)
Other noninterest income   15 17 3 7 32 39 42 5 33 35 72 49          
Noninterest expense 139 129 131 138 138 139 179 122 139 388 158 174 197 276 276 536 579 918
Income (loss) before income taxes 69 45 71 74 50 15 (38) 38 (118) (248) 14 61 23 129 124 240 (103) (149)
Provision (benefit) for income taxes 22 12 24 28 18 4 (10) 12 (40) (410) 0 (6) 0 43 46 82 (34) (416)
Net income (loss) $ 47     46   11 (28) 26 (78) 162 14 67 23 $ 86 $ 78 158 (69) 267
Preferred stock dividend/accretion           0 0 0 (1) (2) (1) (1) (1)     $ 0 $ (1) $ (6)
Net income (loss) from continuing operations   $ 33 $ 47 $ 46 $ 32 $ 11 $ (28) $ 26 $ (79) $ 160 $ 13 $ 66 $ 22          
Basic (loss) income per share (in usd per share) $ 0.67 $ 0.45 $ 0.70 $ 0.69 $ 0.43 $ 0.07 $ (0.61) $ 0.33 $ (1.51) $ 2.79 $ 0.16 $ 1.11 $ 0.33 $ 1.23 $ 1.12 $ 2.27 $ (1.72) $ 4.40
Diluted (loss) income per share (in usd per share) $ 0.66 $ 0.44 $ 0.69 $ 0.68 $ 0.43 $ 0.07 $ (0.61) $ 0.33 $ (1.51) $ 2.77 $ 0.16 $ 1.10 $ 0.33 $ 1.21 $ 1.11 $ 2.24 $ (1.72) $ 4.37