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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Loans	$ 2,678	$ 2,452	$ 7,952	$ 7,025
Investment Securities	617	584	1,866	1,653
Borrowed Funds	468	421	1,433	1,173
Other	342	301	1,017	880
Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contracts [Member] \| Borrowed Funds [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	(271)	107	(1,068)	577
Derivatives	235	(137)	948	(632)
Amounts related to interest settlements on derivatives	16	24	36	57
Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contracts [Member] \| Investment Securities [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	76	(31)	250	(145)
Derivatives	(73)	30	(241)	149
Amounts related to interest settlements on derivatives	4	2	14
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contracts [Member] \| Loans [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI	2	6	(18)	43
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contracts [Member] \| Other [Member] \| Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI		1	18	8
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contracts [Member] \| Investment Securities [Member] \| Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gains (losses) reclassified from AOCI	$ 3	$ 2	$ 5	$ 9

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