Segment Information - Financial Information by Business Segment (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Summary of Operations
Net interest income	$ 138		$ 115		$ 264	$ 221
Net gain (loss) on loan sales	75		63		124	123
Other noninterest income (loss)	93		60		153	111
Total net interest income and noninterest income (loss)	306		238		541	455
(Provision) benefit for loan losses	(17)		1		(17)	1
Compensation and benefits	(90)		(80)		(177)	(160)
Other noninterest expense and directly allocated overhead	(124)		(97)		(228)	(190)
Total noninterest expense	(214)		(177)		(405)	(350)
Income (loss) before indirect overhead allocations and income taxes	75		62		119	106
Overhead allocations	0		0		0	0
(Provision) benefit for income taxes	(14)		(12)		(22)	(21)
Net income	61	$ 36	50	$ 35	97	85
Average balances
Loans held-for-sale	3,539		4,170		3,403	4,201
Loans with government guarantees	502		280		478	285
Loans held-for-investment	10,644		8,416		9,925	7,973
Total assets	19,966		17,784		19,206	17,439
Deposits	14,160		10,414		13,536	9,895
Intersegment Eliminations
Summary of Operations
Total net interest income and noninterest income (loss)	0		0		0	0
Community Banking
Summary of Operations
Net interest income	108		78		211	147
Net gain (loss) on loan sales	(9)		(5)		(15)	(7)
Other noninterest income (loss)	15		9		27	17
Total net interest income and noninterest income (loss)	114		82		223	157
(Provision) benefit for loan losses	(16)		0		(17)	(1)
Compensation and benefits	(24)		(18)		(48)	(35)
Other noninterest expense and directly allocated overhead	(46)		(27)		(87)	(53)
Total noninterest expense	(70)		(45)		(135)	(88)
Income (loss) before indirect overhead allocations and income taxes	28		37		71	68
Overhead allocations	(10)		(9)		(20)	(20)
(Provision) benefit for income taxes	(4)		(7)		(11)	(11)
Net income	14		21		40	37
Average balances
Loans held-for-sale	19		12		45	12
Loans with government guarantees	0		0		0	0
Loans held-for-investment	10,594		8,378		9,879	7,936
Total assets	11,061		8,593		10,323	8,117
Deposits	10,238		8,632		10,112	8,145
Community Banking | Intersegment Eliminations
Summary of Operations
Total net interest income and noninterest income (loss)	(8)		(1)		(12)	(2)
Mortgage Originations
Summary of Operations
Net interest income	23		33		46	64
Net gain (loss) on loan sales	84		68		139	130
Other noninterest income (loss)	19		27		35	46
Total net interest income and noninterest income (loss)	126		128		220	240
(Provision) benefit for loan losses	(1)		(1)		(1)	(1)
Compensation and benefits	(28)		(28)		(52)	(57)
Other noninterest expense and directly allocated overhead	(53)		(47)		(89)	(88)
Total noninterest expense	(81)		(75)		(141)	(145)
Income (loss) before indirect overhead allocations and income taxes	44		52		78	94
Overhead allocations	(10)		(17)		(20)	(35)
(Provision) benefit for income taxes	(7)		(7)		(12)	(12)
Net income	27		28		46	47
Average balances
Loans held-for-sale	3,520		4,158		3,358	4,189
Loans with government guarantees	502		280		478	285
Loans held-for-investment	21		9		17	8
Total assets	5,045		5,225		4,836	5,375
Deposits	0		0		0	0
Mortgage Originations | Intersegment Eliminations
Summary of Operations
Total net interest income and noninterest income (loss)	9		2		16	2
Mortgage Servicing
Summary of Operations
Net interest income	3		1		6	3
Net gain (loss) on loan sales	0		0		0	0
Other noninterest income (loss)	38		22		73	41
Total net interest income and noninterest income (loss)	41		23		79	44
(Provision) benefit for loan losses	0		0		0	0
Compensation and benefits	(6)		(5)		(12)	(9)
Other noninterest expense and directly allocated overhead	(24)		(15)		(49)	(31)
Total noninterest expense	(30)		(20)		(61)	(40)
Income (loss) before indirect overhead allocations and income taxes	11		3		18	4
Overhead allocations	(4)		(5)		(9)	(10)
(Provision) benefit for income taxes	(2)		2		(2)	2
Net income	5		0		7	(4)
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	48		26		52	31
Deposits	3,501		1,782		3,017	1,662
Mortgage Servicing | Intersegment Eliminations
Summary of Operations
Total net interest income and noninterest income (loss)	6		4		12	9
Other
Summary of Operations
Net interest income	4		3		1	7
Net gain (loss) on loan sales	0		0		0	0
Other noninterest income (loss)	21		2		18	7
Total net interest income and noninterest income (loss)	25		5		19	14
(Provision) benefit for loan losses	0		2		1	3
Compensation and benefits	(32)		(29)		(65)	(59)
Other noninterest expense and directly allocated overhead	(1)		(8)		(3)	(18)
Total noninterest expense	(33)		(37)		(68)	(77)
Income (loss) before indirect overhead allocations and income taxes	(8)		(30)		(48)	(60)
Overhead allocations	24		31		49	65
(Provision) benefit for income taxes	(1)		0		3	0
Net income	15		1		4	5
Average balances
Loans held-for-sale	0		0		0	0
Loans with government guarantees	0		0		0	0
Loans held-for-investment	29		29		29	29
Total assets	3,812		3,940		3,995	3,916
Deposits	421		0		407	88
Other | Intersegment Eliminations
Summary of Operations
Total net interest income and noninterest income (loss)	$ (7)		$ (5)		$ (16)	$ (9)