Loans Held-for-Investment - Changes in ALLL by Class of Loan (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 202	$ 229	$ 252	$ 107
(Benefit) provision	(25)	28	(87)	132
Charge-offs	(8)	(4)	(15)	(12)
Recoveries	2	2	21	5
Ending allowance balance	171	255	171	255	$ 107
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				23
Ending allowance balance					$ 23
Consumer loans | Residential first mortgage loans
Allowance for Loan Losses [Roll Forward]
Beginning balance	48	60	49	22
(Benefit) provision	(5)	(6)	(4)	10
Charge-offs	(1)	(2)	(4)	(5)
Recoveries	1	0	2	0
Ending allowance balance	43	52	43	52	22
Consumer loans | Residential first mortgage loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				25
Ending allowance balance					25
Consumer loans | Home equity
Allowance for Loan Losses [Roll Forward]
Beginning balance	17	28	25	14
(Benefit) provision	(3)	1	(10)	3
Charge-offs	0	(1)	(1)	(3)
Recoveries	1	1	1	3
Ending allowance balance	15	29	15	29	14
Consumer loans | Home equity | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				12
Ending allowance balance					12
Consumer loans | Other consumer
Allowance for Loan Losses [Roll Forward]
Beginning balance	38	34	39	6
(Benefit) provision	(5)	4	(6)	24
Charge-offs	(1)	(1)	(3)	(4)
Recoveries	0	1	2	2
Ending allowance balance	32	38	32	38	6
Consumer loans | Other consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				10
Ending allowance balance					10
Commercial loans | Commercial real estate
Allowance for Loan Losses [Roll Forward]
Beginning balance	58	83	84	38
(Benefit) provision	(23)	6	(49)	65
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending allowance balance	35	89	35	89	38
Commercial loans | Commercial real estate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				(14)
Ending allowance balance					(14)
Commercial loans | Commercial and industrial
Allowance for Loan Losses [Roll Forward]
Beginning balance	38	23	51	22
(Benefit) provision	11	19	(17)	26
Charge-offs	(6)	0	(7)	0
Recoveries	0	0	16	0
Ending allowance balance	43	42	43	42	22
Commercial loans | Commercial and industrial | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				(6)
Ending allowance balance					(6)
Commercial loans | Warehouse lending
Allowance for Loan Losses [Roll Forward]
Beginning balance	3	1	4	5
(Benefit) provision	0	4	(1)	4
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending allowance balance	$ 3	$ 5	$ 3	5	5
Commercial loans | Warehouse lending | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
Beginning balance				$ (4)
Ending allowance balance					$ (4)