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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net gains recognized in OCI	$ 83	$ 240	$ 624	$ 351
Amount of pre-tax net gains (losses) reclassified from OCI into net income	$ 62	$ (1)	$ 94	$ (3)