Fair Value of Assets and Liabilities - Gains/(losses) on Nonrecurring Fair Value Measurements (Details) - Non Recurring - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans, net of unearned income	$ (1)	$ (1)	$ (3)	$ (6)
Net gains/(losses), OREO	(1)	0	(1)	0
Net gains/(losses), Other assets	0	(1)	0	(1)
Gain (loss) on financial assets measured on non-recurring basis	(4)	(3)	(6)	(9)
SBAs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans held for sale	$ (2)	$ (1)	$ (2)	$ (2)