Derivatives and Hedging Activities - Fair Values, Volume of Activity and Gain (Loss) Information Related to Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional Amount	$ 126,077	$ 102,645
Derivative assets, Netting adjustments	(473)	(333)
Derivative assets, Fair Value	778	529
Derivative liabilities, Netting adjustments	(335)	(337)
Derivative liabilities, Fair Value	156	353
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	39,208	28,668
Derivative assets, Fair Value	191	52
Derivative liabilities, Fair Value	20	(10)
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	86,869	73,977
Derivative assets, Fair Value	1,062	812
Derivative liabilities, Fair Value	513	733
Interest Rate [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	39,208	28,546
Derivative assets, Fair Value	191	50
Derivative liabilities, Fair Value	20	(10)
Interest Rate [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	71,209	63,454
Derivative assets, Fair Value	772	365
Derivative liabilities, Fair Value	233	307
Foreign Exchange Contract [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	122
Derivative assets, Fair Value	0	2
Derivative liabilities, Fair Value	0	0
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	6,572	6,829
Derivative assets, Fair Value	67	104
Derivative liabilities, Fair Value	60	95
Commodity [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	5,324	2,002
Derivative assets, Fair Value	208	333
Derivative liabilities, Fair Value	200	323
Credit [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	427	226
Derivative assets, Fair Value	1	1
Derivative liabilities, Fair Value	10	1
Other [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,337	1,466
Derivative assets, Fair Value	14	9
Derivative liabilities, Fair Value	10	7
Net Derivatives [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	126,077	102,645
Derivative assets, Fair Value	780	531
Derivative liabilities, Fair Value	198	386
Counterparty And Cash Collateral Netting [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	0
Derivative assets, Fair Value	(2)	(2)
Derivative liabilities, Fair Value	$ (42)	$ (33)

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