Risk Management - Effect of Derivative Contracts on the Income Statement (Details) - Derivatives designated as hedging instruments - Derivatives in fair value hedging relationships - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Interest rate contracts | Interest, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in income on derivative and related hedged item	$ 433	$ 128
Hedged fixed rate debt
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease)	799
Hedged fixed rate debt | Interest, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in income on derivative and related hedged item	$ (440)	$ (138)