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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net gains recognized in OCI	$ 611	$ 348	$ 214
Amount of pre-tax net gains (losses) reclassified from OCI into net income	$ 237	$ 16	$ (2)