Variable Interest Entities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity
Assets	$ 204,680,000,000	$ 169,369,000,000
Lower limit
Variable Interest Entity
Unfunded commitments, year expected to be funded	2021
Upper Limit
Variable Interest Entity
Unfunded commitments, year expected to be funded	2036
Variable Interest Entity, Primary Beneficiary | Automobile loan
Variable Interest Entity
Carry value of automobile loans securitized		1,430,000,000
Face amount of notes issued or redeemed		1,370,000,000
Long-term debt retained		68,000,000
Assets	$ 809,000,000	1,429,000,000
Variable Interest Entity, Not Primary Beneficiary | Loans provided to VIEs
Variable Interest Entity
Unfunded commitment amounts	1,200,000,000	1,400,000,000
Variable Interest Entity, Not Primary Beneficiary | CDC investments
Variable Interest Entity
Assets	1,546,000,000	1,435,000,000
Variable Interest Entity, Not Primary Beneficiary | CDC investments | Qualified Affordable Housing Tax Credits
Variable Interest Entity
Assets	1,300,000,000	1,200,000,000
Unfunded commitments in qualifying LIHTC investments	478,000,000	428,000,000
Variable Interest Entity, Not Primary Beneficiary | Private equity investments
Variable Interest Entity
Assets	117,000,000	89,000,000
Unfunded commitment amounts	83,000,000	75,000,000
Capital contribution to private equity investments	19,000,000	12,000,000
OTTI associated with nonconforming investments affected by the Volcker Rule	$ 0	$ 0	$ 8,000,000