Financial Derivatives (Gains (Losses) on Derivatives Not Designated As Hedging Instruments under GAAP) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	$ 820	$ 507	$ 415
Mortgage Banking | Interest Rate Contract
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	792	405	(56)
Customer-related Contracts
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	366	239	203
Customer-related Contracts | Interest Rate Contract
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	210	125	99
Customer-related Contracts | Foreign Exchange And Other Contract
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	156	114	104
Other Risk Management Activity | Foreign Exchange And Other Contract
Derivative [Line Items]
Total gains (losses) from derivatives not designated as hedging instruments	$ (338)	$ (137)	$ 268