Derivative Financial Instruments - Net Gains (Losses) Relating to Derivative Instruments Designated as Cash Flow Hedges (Details) - Cash Flow Hedging - Interest Income (Expense) Net - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net gains recognized in OCI	$ 1	$ 105	$ 625	$ 456
Amount of pre-tax net gains reclassified from OCI into net income	$ 72	$ 5	$ 165	$ 2