Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended		12 Months Ended
	Jan. 01, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at the end of the prior period	$ 68	$ 178	$ 197	$ 161	$ 68	$ 197	$ 68	$ 68
Liability for credit losses on contingent guarantees at the end of the prior period			0		0			0	$ 7
Balance at beginning of period		152	178	198	161	152	198	197	68
Provision (credit) for losses on off balance sheet exposures		(26)		37		(45)	57
Balance at end of period		152	178	198	161	152	198	197	68
Impact of ASC 326 Adoption
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Cumulative effect from changes in accounting principle			0		0			0	66
Cumulative Effect, Period of Adoption, Adjusted Balance
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at the end of the prior period	141	$ 178	197	$ 161	141	$ 197	$ 141	141
Balance at beginning of period			178		161			197	141
Balance at end of period			$ 178		$ 161			$ 197	$ 141
Other Financial Assets | Impact of ASC 326 Adoption
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Cumulative effect from changes in accounting principle	$ 4