Fair Value of Assets and Liabilities - Gains/(losses) on Nonrecurring Fair Value Measurements (Details) - Non Recurring - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans, net of unearned income	$ (7)	$ (5)
Gain (loss) on financial assets measured on non-recurring basis	(8)	(6)
SBAs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains/(losses), Loans held for sale	$ (1)	$ (1)