Derivatives - Gains/(Losses) on Derivatives Associated with Interest Rate Risk Management Activities (Details) - Hedging Instruments And Hedged Items - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Customer Interest Rate Contracts Hedging | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) related to interest rate derivatives	$ 357	$ 92	$ 2
Customer Interest Rate Contracts Hedging | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) related to interest rate derivatives	(357)	(92)	(2)
Debt Hedging | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) related to interest rate derivatives	2	13	(2)
Debt Hedging | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) related to term borrowings	$ (2)	$ (13)	$ 2