Financial Derivatives (Gains (Losses) on Derivatives Not Designated As Hedging Instruments under GAAP) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	$ 874	$ 95
Mortgage Banking [Member] | Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	654	128
Customer Contracts [Member]
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	13	21
Customer Contracts [Member] | Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	2	(2)
Customer Contracts [Member] | Foreign Exchange And Other Contract [Member]
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	11	23
Other Risk Management Activity [Member] | Foreign Exchange And Other Contract [Member]
Derivative [Line Items]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net	$ 207	$ (54)