Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Notional or contractual amount	$ 240,505	$ 255,546
Derivative assets, gross amount	4,101	1,729
Derivative liabilities, gross amount	1,739	1,197
Derivative asset, netting adjustments	(1,622)	(633)
Derivative liability, netting adjustments	(708)	(523)
Total derivative assets	2,479	1,096
Total derivative liabilities	1,031	674
Net valuation allowance on derivative assets and liabilities for non-performance risk	40	12
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	141,130	164,821
Derivative assets, gross amount	957	332
Derivative liabilities, gross amount	201	305
Derivatives designated as accounting hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	132,353	154,487
Derivative assets, gross amount	851	332
Derivative liabilities, gross amount	26	84
Derivatives designated as accounting hedges \| Interest rate contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	49,703	57,587
Derivative assets, gross amount	4	11
Derivative liabilities, gross amount	17	55
Derivatives designated as accounting hedges \| Interest rate contracts \| Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	82,650	96,900
Derivative assets, gross amount	847	321
Derivative liabilities, gross amount	9	29
Derivatives designated as accounting hedges \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	8,777	10,334
Derivative assets, gross amount	106	0
Derivative liabilities, gross amount	175	221
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,465	1,402
Derivative assets, gross amount	90	0
Derivative liabilities, gross amount	0	6
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	4,495	6,103
Derivative assets, gross amount	13	0
Derivative liabilities, gross amount	99	113
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	2,817	2,829
Derivative assets, gross amount	3	0
Derivative liabilities, gross amount	76	102
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	99,375	90,725
Derivative assets, gross amount	3,144	1,397
Derivative liabilities, gross amount	1,538	892
Derivatives not designated as accounting hedges \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	89,408	82,434
Derivative assets, gross amount	3,049	1,349
Derivative liabilities, gross amount	1,467	853
Derivatives not designated as accounting hedges \| Interest rate contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	68,343	62,268
Derivative assets, gross amount	1,623	552
Derivative liabilities, gross amount	198	117
Derivatives not designated as accounting hedges \| Interest rate contracts \| Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or contractual amount	7,300	6,729
Derivative assets, gross amount	90	48
Derivative liabilities, gross amount	66	30
Derivatives not designated as accounting hedges \| Foreign exchange contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	3,677	4,674
Derivative assets, gross amount	47	39
Derivative liabilities, gross amount	50	42
Derivatives not designated as accounting hedges \| Commodity contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	17,388	15,492
Derivative assets, gross amount	1,379	758
Derivative liabilities, gross amount	1,219	694
Derivatives not designated as accounting hedges \| Other contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	2,667	1,562
Derivative assets, gross amount	5	0
Derivative liabilities, gross amount	$ 5	$ 9

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Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, and obligation to return cash collateral under master netting arrangements.

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