Variable Interest Entities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Variable Interest Entity
Assets	$ 202,906		$ 202,906		$ 169,369
Upper limit
Variable Interest Entity
Unfunded commitments, year expected to be funded			2035
Variable Interest Entity, Primary Beneficiary | Automobile loan
Variable Interest Entity
Carry value of automobile loans securitized					1,430
Face amount of notes issued or redeemed					1,370
Long-term debt retained					68
Assets	1,091		$ 1,091		1,429
Variable Interest Entity, Not Primary Beneficiary | Loans provided to VIEs
Variable Interest Entity
Unfunded commitment amounts			1,300		1,400
Variable Interest Entity, Not Primary Beneficiary | CDC investments
Variable Interest Entity
Assets	1,452		1,452		1,435
Variable Interest Entity, Not Primary Beneficiary | CDC investments | Qualified Affordable Housing Tax Credits
Variable Interest Entity
Assets	1,200		1,200		1,200
Unfunded commitments in qualifying LIHTC investments	424		424		428
Variable Interest Entity, Not Primary Beneficiary | Private equity investments
Variable Interest Entity
Assets	91		91		89
Unfunded commitment amounts			80		$ 75
Capital contribution to private equity investments	$ 1	$ 5	$ 5	$ 7