Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Notional or contractual amount	$ 232,327	$ 255,546
Derivative assets, gross amount	3,415	1,729
Derivative liabilities, gross amount	1,518	1,197
Derivative asset, netting adjustments	(1,148)	(633)
Derivative liability, netting adjustments	(739)	(523)
Total derivative assets	2,267	1,096
Total derivative liabilities	779	674
Net valuation allowance on derivative assets and liabilities for non-performance risk	31	12
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	138,724	164,821
Derivative assets, gross amount	921	332
Derivative liabilities, gross amount	368	305
Derivatives designated as accounting hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	129,499	154,487
Derivative assets, gross amount	757	332
Derivative liabilities, gross amount	11	84
Derivatives designated as accounting hedges \| Interest rate contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	47,349	57,587
Derivative assets, gross amount	9	11
Derivative liabilities, gross amount	10	55
Derivatives designated as accounting hedges \| Interest rate contracts \| Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	82,150	96,900
Derivative assets, gross amount	748	321
Derivative liabilities, gross amount	1	29
Derivatives designated as accounting hedges \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	9,225	10,334
Derivative assets, gross amount	164	0
Derivative liabilities, gross amount	357	221
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,527	1,402
Derivative assets, gross amount	164	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	4,582	6,103
Derivative assets, gross amount	0	0
Derivative liabilities, gross amount	161	113
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	3,116	2,829
Derivative assets, gross amount	0	0
Derivative liabilities, gross amount	196	102
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	93,603	90,725
Derivative assets, gross amount	2,494	1,397
Derivative liabilities, gross amount	1,150	892
Derivatives not designated as accounting hedges \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	90,007	82,434
Derivative assets, gross amount	2,422	1,349
Derivative liabilities, gross amount	1,088	853
Derivatives not designated as accounting hedges \| Interest rate contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	68,459	62,268
Derivative assets, gross amount	1,429	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	1,770	6,729
Derivative assets, gross amount	71	48
Derivative liabilities, gross amount	56	30
Derivatives not designated as accounting hedges \| Foreign exchange contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	4,677	4,674
Derivative assets, gross amount	58	39
Derivative liabilities, gross amount	70	42
Derivatives not designated as accounting hedges \| Commodity contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	16,871	15,492
Derivative assets, gross amount	935	758
Derivative liabilities, gross amount	820	694
Derivatives not designated as accounting hedges \| Other contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,826	1,562
Derivative assets, gross amount	1	0
Derivative liabilities, gross amount	$ 6	$ 9

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