Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) segment	Jun. 30, 2021 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment			3
Summary of Operations
Net interest income	$ 193	$ 183	$ 358	$ 371
Provision (benefit) for credit losses	(9)	(44)	(13)	(72)
Net interest income after benefit for credit losses	202	227	371	443
Net gain on loan sales	27	168	72	395
Loan fees and charges	29	37	56	79
Net return on mortgage servicing rights	22	(5)	51	(5)
Loan administrative (expense) income	33	28	66	54
Other noninterest income (expense)	20	24	46	53
Total noninterest income	131	252	291	576
Compensation and benefits	122	122	249	266
Commissions	22	51	48	112
Loan processing expense	23	22	44	43
General, administrative and other	89	94	176	215
Total noninterest expense	256	289	517	636
Income (loss) before indirect overhead allocations and income taxes	77	190	145	383
Indirect overhead allocation (expense) income	0	0	0	0
Provision for income taxes	17	43	32	87
Net income	60	147	113	296
Intersegment revenue (expense)	0	0	0	0
Average balances
Loans held-for-sale	3,571	6,902	4,199	7,181
Loans with government guarantees	1,161	2,344	1,281	2,422
Loans held-for-investment	13,339	13,689	12,863	14,299
Total assets	23,867	28,011	24,013	29,032
Deposits	17,488	19,070	17,787	19,554
Other
Summary of Operations
Net interest income	7	(27)	(9)	(55)
Provision (benefit) for credit losses	(16)	(43)	(45)	(55)
Net interest income after benefit for credit losses	23	16	36	0
Net gain on loan sales	0	0	0	0
Loan fees and charges	0	0	0	0
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	(3)	(3)	(6)	(6)
Other noninterest income (expense)	6	7	13	14
Total noninterest income	3	4	7	8
Compensation and benefits	39	32	77	80
Commissions	0	0	0	0
Loan processing expense	1	0	2	2
General, administrative and other	28	52	65	96
Total noninterest expense	68	84	144	178
Income (loss) before indirect overhead allocations and income taxes	(42)	(64)	(101)	(170)
Indirect overhead allocation (expense) income	35	30	66	64
Provision for income taxes	4	(4)	0	(16)
Net income	(11)	(30)	(35)	(90)
Average balances
Loans held-for-sale	0	0	1	0
Loans with government guarantees	0	0	0	0
Loans held-for-investment	(4)	24	(3)	27
Total assets	3,964	3,547	3,969	3,520
Deposits	946	1,174	985	1,121
Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	(29)	(55)	(69)	(78)
Community Banking | Operating Segments
Summary of Operations
Net interest income	136	149	258	305
Provision (benefit) for credit losses	13	1	35	(13)
Net interest income after benefit for credit losses	123	148	223	318
Net gain on loan sales	0	0	0	0
Loan fees and charges	0	0	0	1
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	(1)	0	(1)	0
Other noninterest income (expense)	19	15	37	34
Total noninterest income	18	15	36	35
Compensation and benefits	28	25	56	51
Commissions	0	1	1	1
Loan processing expense	1	2	3	3
General, administrative and other	34	1	52	33
Total noninterest expense	63	29	112	88
Income (loss) before indirect overhead allocations and income taxes	78	134	147	265
Indirect overhead allocation (expense) income	(12)	(9)	(22)	(19)
Provision for income taxes	11	26	23	52
Net income	55	99	102	194
Average balances
Loans held-for-sale	5	22	11	11
Loans with government guarantees	0	0	0	0
Loans held-for-investment	11,577	11,827	11,261	12,314
Total assets	11,962	12,175	11,646	12,668
Deposits	11,744	11,694	11,874	11,749
Community Banking | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	14	45	36	59
Mortgage Originations | Operating Segments
Summary of Operations
Net interest income	46	58	102	114
Provision (benefit) for credit losses	(6)	(2)	(3)	(4)
Net interest income after benefit for credit losses	52	60	105	118
Net gain on loan sales	27	168	72	395
Loan fees and charges	7	18	13	41
Net return on mortgage servicing rights	22	(5)	51	(5)
Loan administrative (expense) income	(7)	(9)	(14)	(20)
Other noninterest income (expense)	(5)	2	(4)	5
Total noninterest income	44	174	118	416
Compensation and benefits	37	49	82	103
Commissions	22	50	47	111
Loan processing expense	9	12	18	23
General, administrative and other	4	20	15	42
Total noninterest expense	72	131	162	279
Income (loss) before indirect overhead allocations and income taxes	24	103	61	255
Indirect overhead allocation (expense) income	(16)	(16)	(31)	(35)
Provision for income taxes	0	18	4	46
Net income	8	69	26	174
Average balances
Loans held-for-sale	3,566	6,880	4,187	7,170
Loans with government guarantees	1,161	2,344	1,282	2,422
Loans held-for-investment	1,766	1,838	1,605	1,958
Total assets	7,807	12,021	8,248	12,515
Deposits	34	23	38	19
Mortgage Originations | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	5	(1)	14	(3)
Mortgage Servicing | Operating Segments
Summary of Operations
Net interest income	4	3	7	7
Provision (benefit) for credit losses	0	0	0	0
Net interest income after benefit for credit losses	4	3	7	7
Net gain on loan sales	0	0	0	0
Loan fees and charges	22	19	43	37
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	44	40	87	80
Other noninterest income (expense)	0	0	0	0
Total noninterest income	66	59	130	117
Compensation and benefits	18	16	34	32
Commissions	0	0	0	0
Loan processing expense	12	8	21	15
General, administrative and other	23	21	44	44
Total noninterest expense	53	45	99	91
Income (loss) before indirect overhead allocations and income taxes	17	17	38	33
Indirect overhead allocation (expense) income	(7)	(5)	(13)	(10)
Provision for income taxes	2	3	5	5
Net income	8	9	20	18
Average balances
Loans held-for-sale	0	0	0	0
Loans with government guarantees	0	0	(1)	0
Loans held-for-investment	0	0	0	0
Total assets	134	268	150	329
Deposits	4,764	6,179	4,890	6,665
Mortgage Servicing | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	$ 10	$ 11	$ 19	$ 22