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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net (losses) gains recognized in OCI	$ 11	$ 83	$ (70)	$ 624
Amount of pre-tax net gains reclassified from OCI into net income	$ 73	$ 62	$ 146	$ 94