Segment Information (Details)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2016
USD ($)
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Sep. 30, 2014
USD ($)
Jun. 30, 2014
USD ($)
Mar. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Sep. 30, 2013
USD ($)
Jun. 30, 2013
USD ($)
Mar. 31, 2013
USD ($)
Jun. 30, 2016
USD ($)
segment
Jun. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
segment
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Segment Reporting Information [Line Items]                                    
Number of business segments | segment                           4   4    
Summary of Operations                                    
Net interest income $ 77 $ 76 $ 73 $ 73 $ 65 $ 61 $ 64 $ 63 $ 58 $ 41 $ 43 $ 47 $ 56 $ 156 $ 138 $ 287 $ 247 $ 186
Net gain on loan sales 90 46 68 83 91 53 52 55 45 45 75 144 137 165 174 288 206 402
Representation and warranty (provision) benefit 4 6 6 5 2 6 (13) (5) 2 15 (5) (29) (17) 6 7 19 (10) (36)
Other noninterest income 34     38                   62 64      
Benefit (provision) for loan losses 3 1 1 13 4 (5) (8) (6) (112) (14) (4) (31) (21) 16 17 19 (132) (70)
Asset resolution (1)     (5)                   (4) (13) (15) (57) (52)
Depreciation and amortization expense (8)     (5)                   (15) (11)      
Other noninterest expense (130)     (128)                   (257) (252)      
Total noninterest expense (139)     (138)                   (276) (276)      
Income (loss) before income taxes 69 45 71 74 50 15 (38) 38 (118) (248) 14 61 23 129 124 240 (103) (149)
Provision 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
Average balances                                    
Loans with government guarantees 2,884     2,218                   2,897 2,031 2,188 1,554 2,548
Loans held-for-investment                               633 1,216 1,477
Total assets 5,569     4,938                   5,618 4,617 5,076 4,122 4,411
Total assets 13,438     11,811                   13,491 11,336 11,956 9,886 12,555
Average Loans With Government Guarantees 444     630                   460 747      
Deposits 8,631     7,736                   8,341 7,553 7,877 6,734 7,373
Mortgage Origination                                    
Summary of Operations                                    
Net interest income 20     19                   40 34      
Net gain on loan sales 87     87                   156 183      
Representation and warranty (provision) benefit 4     5                   6 7      
Other noninterest income 9     24                   13 34      
Benefit (provision) for loan losses 0     0                   0 0      
Asset resolution 0     0                   0 0      
Depreciation and amortization expense (1)     0                   (2) (1)      
Other noninterest expense (61)     (61)                   (118) (118)      
Total noninterest expense (62)     (61)                   (120) (119)      
Income (loss) before income taxes 58     74                   95 139      
Provision for income taxes 0     0                   0 0      
Net income (loss) 58     74                   95 139      
Average balances                                    
Loans with government guarantees 2,828     2,173                   2,780 1,988 2,148 1,472 2,312
Loans held-for-investment                               0 0 12
Total assets 3     2                   7 2 4 1 0
Total assets 3,471     2,628                   3,409 2,477 2,661 1,630 3,277
Average Loans With Government Guarantees 0     0                   0 0      
Deposits 0     0                   0 0 0 0 0
Mortgage Servicing                                    
Summary of Operations                                    
Net interest income 7     4                   13 7      
Net gain on loan sales 0     0                   0 0      
Representation and warranty (provision) benefit 0     0                   0 0      
Other noninterest income 13     14                   26 27      
Benefit (provision) for loan losses 0     0                   0 0      
Asset resolution (1)     (5)                   (4) (12)      
Depreciation and amortization expense (1)     0                   (2) (1)      
Other noninterest expense (21)     (28)                   (45) (53)      
Total noninterest expense (23)     (33)                   (51) (66)      
Income (loss) before income taxes (3)     (15)                   (12) (32)      
Provision for income taxes 0     0                   0 0      
Net income (loss) (3)     (15)                   (12) (32)      
Average balances                                    
Loans with government guarantees 0     0                   0 0 0 20 49
Loans held-for-investment                               633 1,216 1,465
Total assets 0     0                   0 0 0 0 0
Total assets 678     986                   703 1,077 944 1,349 1,699
Average Loans With Government Guarantees 444     630                   460 747      
Deposits 1,558     1,128                   1,357 1,038 1,203 750 837
Community Banking                                    
Summary of Operations                                    
Net interest income 49     42                   96 81      
Net gain on loan sales 3     (4)                   9 (9)      
Representation and warranty (provision) benefit 0     0                   0 0      
Other noninterest income 6     1                   13 8      
Benefit (provision) for loan losses 3     13                   16 17      
Asset resolution 0     0                   0 (1)      
Depreciation and amortization expense (2)     (2)                   (4) (3)      
Other noninterest expense (45)     (37)                   (88) (77)      
Total noninterest expense (47)     (39)                   (92) (81)      
Income (loss) before income taxes 14     13                   42 16      
Provision for income taxes 0     0                   0 0      
Net income (loss) 14     13                   42 16      
Average balances                                    
Loans with government guarantees 56     45                   117 43 40 62 187
Loans held-for-investment                               0 0 0
Total assets 5,566     4,831                   5,611 4,500 4,986 3,975 4,325
Total assets 5,653     4,803                   5,745 4,457 4,972 3,943 4,509
Average Loans With Government Guarantees 0     0                   0 0      
Deposits 7,073     6,608                   6,984 6,515 6,674 5,984 6,529
Other                                    
Summary of Operations                                    
Net interest income 1     8                   7 16      
Net gain on loan sales 0     0                   0 0      
Representation and warranty (provision) benefit 0     0                   0 0      
Other noninterest income 6     (1)                   10 (5)      
Benefit (provision) for loan losses 0     0                   0 0      
Asset resolution 0     0                   0 0      
Depreciation and amortization expense (4)     (3)                   (7) (6)      
Other noninterest expense (3)     (2)                   (6) (4)      
Total noninterest expense (7)     (5)                   (13) (10)      
Income (loss) before income taxes 0     2                   4 1      
Provision for income taxes (22)     (28)                   (43) (46)      
Net income (loss) (22)     (26)                   (39) (45)      
Average balances                                    
Loans with government guarantees 0     0                   0 0 0 0 0
Loans held-for-investment                               0 0 0
Total assets 0     105                   0 115 86 146 86
Total assets 3,636     3,394                   3,634 3,325 3,379 2,964 3,070
Average Loans With Government Guarantees 0     0                   0 0      
Deposits 0     0                   0 0 0 0 7
Operating Segments                                    
Summary of Operations                                    
Net interest income                               287 247 186
Net gain on loan sales                               288 206 402
Representation and warranty (provision) benefit                               19 (10) (36)
Other noninterest income                               163 165 287
Total net interest income and noninterest income 205     199                   389 383 757 608 839
Benefit (provision) for loan losses                               19 (132) (70)
Asset resolution                               (15) (57) (52)
Depreciation and amortization expense                               (24) (24) (23)
Other noninterest expense                               (497) (498) (843)
Total noninterest expense                               (536) (579) (918)
Income (loss) before income taxes                               240 (103) (149)
Provision for income taxes                               (82) 34 416
Net income (loss)                               158 (69) 267
Operating Segments | Mortgage Origination                                    
Summary of Operations                                    
Net interest income                               72 56 74
Net gain on loan sales                               303 209 401
Representation and warranty (provision) benefit                               19 (10) (36)
Other noninterest income                               78 70 149
Total net interest income and noninterest income 120     135                   215 258 472 325 588
Benefit (provision) for loan losses                               0 0 0
Asset resolution                               (1) (3) (6)
Depreciation and amortization expense                               (3) (1) (1)
Other noninterest expense                               (228) (206) (351)
Total noninterest expense                               (232) (210) (358)
Income (loss) before income taxes                               240 115 230
Provision for income taxes                               0 0 0
Net income (loss)                               240 115 230
Operating Segments | Mortgage Servicing                                    
Summary of Operations                                    
Net interest income                               13 20 32
Net gain on loan sales                               0 0 0
Representation and warranty (provision) benefit                               0 0 0
Other noninterest income                               56 58 62
Total net interest income and noninterest income 20     18                   39 34 69 78 94
Benefit (provision) for loan losses                               0 0 0
Asset resolution                               (13) (50) (55)
Depreciation and amortization expense                               (3) (6) (6)
Other noninterest expense                               (107) (123) (113)
Total noninterest expense                               (123) (179) (174)
Income (loss) before income taxes                               (54) (101) (80)
Provision for income taxes                               0 0 0
Net income (loss)                               (54) (101) (80)
Operating Segments | Community Banking                                    
Summary of Operations                                    
Net interest income                               171 150 160
Net gain on loan sales                               (15) (3) 1
Representation and warranty (provision) benefit                               0 0 0
Other noninterest income                               25 22 27
Total net interest income and noninterest income 58     39                   118 80 181 169 188
Benefit (provision) for loan losses                               19 (132) (70)
Asset resolution                               (1) (4) 9
Depreciation and amortization expense                               (6) (5) (4)
Other noninterest expense                               (153) (158) (186)
Total noninterest expense                               (160) (167) (181)
Income (loss) before income taxes                               40 (130) (63)
Provision for income taxes                               0 0 0
Net income (loss)                               40 (130) (63)
Operating Segments | Other                                    
Summary of Operations                                    
Net interest income                               31 21 (80)
Net gain on loan sales                               0 0 0
Representation and warranty (provision) benefit                               0 0 0
Other noninterest income                               4 15 49
Total net interest income and noninterest income 7     7                   17 11 35 36 (31)
Benefit (provision) for loan losses                               0 0 0
Asset resolution                               0 0 0
Depreciation and amortization expense                               (12) (12) (12)
Other noninterest expense                               (9) (11) (193)
Total noninterest expense                               (21) (23) (205)
Income (loss) before income taxes                               14 13 (236)
Provision for income taxes                               (82) 34 416
Net income (loss)                               (68) 47 180
Intersegment Eliminations                                    
Summary of Operations                                    
Total net interest income and noninterest income 0     0                   0 0 0 0 0
Intersegment Eliminations | Mortgage Origination                                    
Summary of Operations                                    
Total net interest income and noninterest income 1     12                   2 19 10 (2) (32)
Intersegment Eliminations | Mortgage Servicing                                    
Summary of Operations                                    
Total net interest income and noninterest income 6     (2)                   11 1 17 18 51
Intersegment Eliminations | Community Banking                                    
Summary of Operations                                    
Total net interest income and noninterest income 0     (5)                   (1) (10) (15) (3) 3
Intersegment Eliminations | Other                                    
Summary of Operations                                    
Total net interest income and noninterest income $ (7)     $ (5)                   $ (12) $ (10) $ (12) $ (13) $ (22)