Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segments	Sep. 30, 2020 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segments			3
Summary of Operations
Net interest income	$ 195	$ 180	$ 566	$ 496
Provision (benefit) for credit losses	(23)	32	(95)	148
Net interest income after provision for credit losses	218	148	661	348
Net gain on loan sales	169	346	564	739
Loan fees and charges	33	41	112	102
Net return on mortgage servicing rights	9	12	4	10
Loan administrative (expense) income	31	26	85	59
Other noninterest income	24	23	77	68
Total noninterest income	266	448	842	978
Compensation and benefits	130	123	396	341
Commissions	44	72	156	162
Loan processing expense	22	20	65	59
Other noninterest expense	90	86	305	265
Total noninterest expense	286	301	922	827
Income (loss) before indirect overhead allocations and income taxes	198	295	581	499
Indirect overhead allocation (expense) income	0	0	0	0
Provision (benefit) for income taxes	46	73	133	115
Net income	152	222	448	384
Average balances
Loans held-for-sale	7,839	5,602	7,403	5,499
Loans with government guarantees	2,046	2,122	2,295	1,267
Loans held-for-investment	13,540	14,839	14,043	13,424
Total assets	28,047	28,277	28,701	25,992
Deposits	19,686	19,561	19,598	17,698
Other
Summary of Operations
Net interest income	(30)	(32)	(85)	(60)
Provision (benefit) for credit losses	(29)	37	(83)	153
Net interest income after provision for credit losses	(1)	(69)	(2)	(213)
Net gain on loan sales	0	0	0	0
Loan fees and charges	0	0	(1)	0
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	(2)	(3)	(8)	(26)
Other noninterest income	5	5	20	20
Total noninterest income	3	2	11	(6)
Compensation and benefits	40	41	117	118
Commissions	0	0	(1)	0
Loan processing expense	1	0	3	2
Other noninterest expense	33	(30)	135	(137)
Total noninterest expense	74	11	254	(17)
Income (loss) before indirect overhead allocations and income taxes	(72)	(78)	(245)	(202)
Indirect overhead allocation (expense) income	25	33	90	91
Provision (benefit) for income taxes	(6)	2	(22)	(13)
Net income	(41)	(47)	(133)	(98)
Average balances
Loans held-for-sale	0	0	0	0
Loans with government guarantees	0	0	(1)	0
Loans held-for-investment	11	30	22	29
Total assets	3,384	4,401	3,475	4,288
Deposits	1,281	967	1,175	767
Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	(44)	24	(123)	116
Community Banking | Operating Segments
Summary of Operations
Net interest income	149	158	454	395
Provision (benefit) for credit losses	8	(2)	(5)	3
Net interest income after provision for credit losses	141	160	459	392
Net gain on loan sales	0	2	0	2
Loan fees and charges	0	0	1	1
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	0	(1)	(1)	(2)
Other noninterest income	16	15	49	43
Total noninterest income	16	16	49	44
Compensation and benefits	26	28	81	79
Commissions	1	1	2	2
Loan processing expense	1	1	4	4
Other noninterest expense	12	63	39	231
Total noninterest expense	40	93	126	316
Income (loss) before indirect overhead allocations and income taxes	117	83	382	120
Indirect overhead allocation (expense) income	(7)	(11)	(26)	(31)
Provision (benefit) for income taxes	23	15	75	19
Net income	87	57	281	70
Average balances
Loans held-for-sale	20	0	14	0
Loans with government guarantees	0	0	0	0
Loans held-for-investment	11,846	12,311	12,156	10,702
Total assets	12,224	12,603	12,518	11,100
Deposits	12,116	11,265	11,872	10,817
Community Banking | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	34	(22)	93	(97)
Mortgage Originations | Operating Segments
Summary of Operations
Net interest income	72	49	186	147
Provision (benefit) for credit losses	(2)	(3)	(7)	(8)
Net interest income after provision for credit losses	74	52	193	155
Net gain on loan sales	169	344	564	737
Loan fees and charges	13	25	55	58
Net return on mortgage servicing rights	9	12	4	10
Loan administrative (expense) income	(7)	(10)	(26)	(25)
Other noninterest income	3	3	8	5
Total noninterest income	187	374	605	785
Compensation and benefits	48	42	151	111
Commissions	43	71	155	160
Loan processing expense	11	11	34	29
Other noninterest expense	23	32	65	114
Total noninterest expense	125	156	405	414
Income (loss) before indirect overhead allocations and income taxes	136	270	393	526
Indirect overhead allocation (expense) income	(14)	(18)	(50)	(45)
Provision (benefit) for income taxes	26	53	72	101
Net income	96	199	271	380
Average balances
Loans held-for-sale	7,819	5,602	7,389	5,499
Loans with government guarantees	2,046	2,122	2,296	1,267
Loans held-for-investment	1,683	2,498	1,865	2,693
Total assets	12,356	11,195	12,462	10,539
Deposits	40	0	26	0
Mortgage Originations | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	0	(12)	(3)	(46)
Mortgage Servicing | Operating Segments
Summary of Operations
Net interest income	4	5	11	14
Provision (benefit) for credit losses	0	0	0	0
Net interest income after provision for credit losses	4	5	11	14
Net gain on loan sales	0	0	0	0
Loan fees and charges	20	16	57	43
Net return on mortgage servicing rights	0	0	0	0
Loan administrative (expense) income	40	40	120	112
Other noninterest income	0	0	0	0
Total noninterest income	60	56	177	155
Compensation and benefits	16	12	47	33
Commissions	0	0	0	0
Loan processing expense	9	8	24	24
Other noninterest expense	22	21	66	57
Total noninterest expense	47	41	137	114
Income (loss) before indirect overhead allocations and income taxes	17	20	51	55
Indirect overhead allocation (expense) income	(4)	(4)	(14)	(15)
Provision (benefit) for income taxes	3	3	8	8
Net income	10	13	29	32
Average balances
Loans held-for-sale	0	0	0	0
Loans with government guarantees	0	0	0	0
Loans held-for-investment	0	0	0	0
Total assets	83	78	246	65
Deposits	6,249	7,329	6,525	6,114
Mortgage Servicing | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	$ 10	$ 10	$ 33	$ 27