Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the end of the prior period	$ 68	$ 64
Liability for credit losses on contingent guarantees at the end of the prior period		7	$ 0
Provision (credit) for losses on off balance sheet exposures	56	4	6
Balance at end of period	197	68	64
Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Cumulative effect from change in accounting principle		66	0
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the end of the prior period	$ 141	64
Balance at end of period		$ 141	$ 64