Loans Held-for-Investment - Changes in ALLL by Class of Loan (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 241	$ 132	$ 107	$ 252	$ 107
(Benefit) provision	(38)	100		(62)	104
Charge-offs	(2)	(5)		(7)	(8)
Recoveries	1	2		19	3
Ending allowance balance	202	229	$ 132	202	229	$ 107
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member			us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			$ 23		23
Ending allowance balance						$ 23
Consumer loans | Residential first mortgage loans
Allowance for Loan Losses [Roll Forward]
Beginning balance	45	46	22	49	22
(Benefit) provision	4	16		1	16
Charge-offs	(1)	(2)		(3)	(3)
Recoveries	0	0		1	0
Ending allowance balance	48	60	46	48	60	22
Consumer loans | Residential first mortgage loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			25		25
Ending allowance balance						25
Consumer loans | Home equity
Allowance for Loan Losses [Roll Forward]
Beginning balance	20	23	14	25	14
(Benefit) provision	(4)	5		(7)	2
Charge-offs	0	(1)		(1)	(2)
Recoveries	1	1		0	2
Ending allowance balance	17	28	23	17	28	14
Consumer loans | Home equity | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			12		12
Ending allowance balance						12
Consumer loans | Other consumer
Allowance for Loan Losses [Roll Forward]
Beginning balance	33	16	6	39	6
(Benefit) provision	6	19		(1)	20
Charge-offs	(1)	(2)		(2)	(3)
Recoveries	0	1		2	1
Ending allowance balance	38	34	16	38	34	6
Consumer loans | Other consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			10		10
Ending allowance balance						10
Commercial loans | Commercial real estate
Allowance for Loan Losses [Roll Forward]
Beginning balance	84	28	38	84	38
(Benefit) provision	(26)	55		(26)	59
Charge-offs	0	0		0	0
Recoveries	0	0		0	0
Ending allowance balance	58	83	28	58	83	38
Commercial loans | Commercial real estate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			(14)		(14)
Ending allowance balance						(14)
Commercial loans | Commercial and industrial
Allowance for Loan Losses [Roll Forward]
Beginning balance	55	18	22	51	22
(Benefit) provision	(17)	5		(28)	7
Charge-offs	0	0		(1)	0
Recoveries	0	0		16	0
Ending allowance balance	38	23	18	38	23	22
Commercial loans | Commercial and industrial | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			(6)		(6)
Ending allowance balance						(6)
Commercial loans | Warehouse lending
Allowance for Loan Losses [Roll Forward]
Beginning balance	4	1	5	4	5
(Benefit) provision	(1)	0		(1)	0
Charge-offs	0	0		0	0
Recoveries	0	0		0	0
Ending allowance balance	$ 3	$ 1	1	$ 3	1	5
Commercial loans | Warehouse lending | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance			$ (4)		$ (4)
Ending allowance balance						$ (4)