Segment Information (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($) segments	Jun. 30, 2020 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segments					3
Summary of Operations
Net interest income	$ 183		$ 168		$ 371	$ 316
Provision (benefit) for credit losses	(44)		102		(72)	116
Net interest income after provision for credit losses	227		66		443	200
Net gain on loan sales	168		303		395	393
Loan fees and charges	37		38		79	61
Net return on mortgage servicing rights	(5)		(8)		(5)	(2)
Loan administrative (expense) income	28		21		54	33
Other noninterest income	24		21		53	44
Total noninterest income	252		375		576	529
Compensation and benefits	122		116		266	218
Commissions	51		61		112	90
Loan processing expense	22		22		43	39
Other noninterest expense	94		94		215	179
Total noninterest expense	289		293		636	526
Income (loss) before indirect overhead allocations and income taxes	190		148		383	203
Indirect overhead allocation (expense) income	0		0		0	0
Provision (benefit) for income taxes	43		32		87	42
Net income	147	$ 149	116	$ 46	296	161
Average balances
Loans held-for-sale	6,902		5,645		7,181	5,447
Loans with government guarantees	2,344		858		2,422	834
Loans held-for-investment	13,689		13,596		14,299	12,709
Total assets	28,011		26,261		29,032	24,837
Deposits	19,070		17,715		19,554	16,755
Other
Summary of Operations
Net interest income	(27)		(25)		(55)	(27)
Provision (benefit) for credit losses	(43)		107		(55)	116
Net interest income after provision for credit losses	16		(132)		0	(143)
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)		(6)		(6)	(22)
Other noninterest income	7		8		14	14
Total noninterest income	4		2		8	(8)
Compensation and benefits	30		43		76	77
Commissions	0		0		0	0
Loan processing expense	0		1		2	2
Other noninterest expense	54		(103)		101	(107)
Total noninterest expense	84		(59)		179	(28)
Income (loss) before indirect overhead allocations and income taxes	(64)		(71)		(171)	(123)
Indirect overhead allocation (expense) income	30		32		64	58
Provision (benefit) for income taxes	(4)		(7)		(16)	(14)
Net income	(30)		(32)		(91)	(51)
Average balances
Loans held-for-sale	0		0		0	0
Loans with government guarantees	0		0		0	0
Loans held-for-investment	24		30		27	29
Total assets	3,547		4,302		3,520	4,231
Deposits	1,174		746		1,121	666
Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	(55)		94		(78)	92
Community Banking | Operating Segments
Summary of Operations
Net interest income	149		133		305	237
Provision (benefit) for credit losses	1		(3)		(13)	5
Net interest income after provision for credit losses	148		136		318	232
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	0		(1)		0	(2)
Other noninterest income	15		12		34	28
Total noninterest income	15		11		35	26
Compensation and benefits	27		24		55	51
Commissions	1		0		1	1
Loan processing expense	2		1		3	3
Other noninterest expense	(1)		124		28	168
Total noninterest expense	29		149		87	223
Income (loss) before indirect overhead allocations and income taxes	134		(2)		266	35
Indirect overhead allocation (expense) income	(9)		(11)		(19)	(20)
Provision (benefit) for income taxes	26		(3)		52	3
Net income	99		(10)		195	12
Average balances
Loans held-for-sale	22		0		11	0
Loans with government guarantees	0		0		0	0
Loans held-for-investment	11,827		10,878		12,314	9,888
Total assets	12,175		11,292		12,668	10,340
Deposits	11,694		10,747		11,749	10,590
Community Banking | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	45		(69)		59	(75)
Mortgage Originations | Operating Segments
Summary of Operations
Net interest income	58		56		114	98
Provision (benefit) for credit losses	(2)		(2)		(4)	(5)
Net interest income after provision for credit losses	60		58		118	103
Net gain on loan sales	168		303		395	393
Loan fees and charges	18		19		41	33
Net return on mortgage servicing rights	(5)		(8)		(5)	(2)
Loan administrative (expense) income	(9)		(8)		(20)	(15)
Other noninterest income	2		1		5	2
Total noninterest income	174		307		416	411
Compensation and benefits	49		38		103	69
Commissions	50		61		111	89
Loan processing expense	12		11		23	18
Other noninterest expense	20		56		42	82
Total noninterest expense	131		166		279	258
Income (loss) before indirect overhead allocations and income taxes	103		199		255	256
Indirect overhead allocation (expense) income	(16)		(15)		(35)	(27)
Provision (benefit) for income taxes	18		39		46	48
Net income	69		145		174	181
Average balances
Loans held-for-sale	6,880		5,645		7,170	5,447
Loans with government guarantees	2,344		858		2,422	834
Loans held-for-investment	1,838		2,688		1,958	2,792
Total assets	12,021		10,598		12,515	10,207
Deposits	23		0		19	0
Mortgage Originations | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	(1)		(34)		(3)	(34)
Mortgage Servicing | Operating Segments
Summary of Operations
Net interest income	3		4		7	8
Provision (benefit) for credit losses	0		0		0	0
Net interest income after provision for credit losses	3		4		7	8
Net gain on loan sales	0		0		0	0
Loan fees and charges	19		19		37	28
Net return on mortgage servicing rights	0		0		0	0
Loan administrative (expense) income	40		36		80	72
Other noninterest income	0		0		0	0
Total noninterest income	59		55		117	100
Compensation and benefits	16		11		32	21
Commissions	0		0		0	0
Loan processing expense	8		9		15	16
Other noninterest expense	21		17		44	36
Total noninterest expense	45		37		91	73
Income (loss) before indirect overhead allocations and income taxes	17		22		33	35
Indirect overhead allocation (expense) income	(5)		(6)		(10)	(11)
Provision (benefit) for income taxes	3		3		5	5
Net income	9		13		18	19
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	268		69		329	59
Deposits	6,179		6,222		6,665	5,499
Mortgage Servicing | Intersegment Eliminations
Summary of Operations
Intersegment revenue (expense)	$ 11		$ 9		$ 22	$ 17