Financial Derivatives (Gains (Losses) Recognized on Fair Value and Cash Flow Hedges in the Consolidated Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Loans	$ 2,116	$ 2,678	$ 6,853	$ 7,952
Investment Securities	490	617	1,599	1,866
Borrowed Funds	118	468	619	1,433
Other	457	342	1,071	1,017
Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member] \| Investment Securities [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	(13)	76	224	250
Derivatives	14	(73)	(219)	(241)
Amounts related to interest settlements on derivatives	(3)	4	(7)	14
Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member] \| Borrowed Funds [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	141	(271)	(1,300)	(1,068)
Derivatives	(166)	235	1,220	948
Amounts related to interest settlements on derivatives	149	16	341	36
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Loans [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI	118	2	262	(18)
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Investment Securities [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI	$ 16	3	19	5
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Other [Member] \| Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI			$ 1	$ 18

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