Fair Value of Assets and Liabilities - Gains/(losses) on Nonrecurring Fair Value Measurements (Details) - Non Recurring - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans, net of unearned income	$ (9)	$ (17)	$ (12)	$ (31)
Net gains/(losses), OREO	0	0	(1)	0
Net gains/(losses), Other assets	(2)	0	(2)	(1)
Gain (loss) on financial assets measured on non-recurring basis	(13)	(19)	(18)	(35)
SBAs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans held for sale	$ (2)	$ (2)	$ (3)	$ (3)