Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Amount		$ 311,611	$ 322,942
Amortized Cost		124,648	118,618
Cash flow hedges
Derivative [Line Items]
Notional Amount		0	0
Fair value hedges | AFS securities (1)
Derivative [Line Items]
Hedged Asset / Liability Basis	[1]	101,804	100,988
Amortized Cost		$ 103,200	$ 99,400

[1] The amortized cost of AFS securities was $103.2 billion at March 31, 2021 and $99.4 billion at December 31, 2020.