Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at the end of the prior period	$ 68	$ 161	$ 62	$ 68	$ 64
Liability for credit losses on contingent guarantees at the end of the prior period						$ 0	$ 7	$ 0	$ 0
Cumulative effect from changes in accounting principle	66
Balance at beginning of period	141	198	64	198	64	$ 161	$ 68	$ 62	$ 64
Provision (credit) for losses on off balance sheet exposures		37	2	57	0
Balance at end of period	141	$ 198	$ 64	$ 198	$ 64
Other Financial Assets
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Cumulative effect from changes in accounting principle	$ 4