Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Notional or contractual amount	$ 269,784	$ 255,546
Derivative assets, gross amount	4,835	1,729
Derivative liabilities, gross amount	2,214	1,197
Derivative asset, netting adjustments	(2,226)	(633)
Derivative liability, netting adjustments	(754)	(523)
Total derivative assets	2,609	1,096
Total derivative liabilities	1,460	674
Net valuation allowance on derivative assets and liabilities for non-performance risk	33	12
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	172,000	164,821
Derivative assets, gross amount	1,102	332
Derivative liabilities, gross amount	110	305
Derivatives designated as accounting hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	163,361	154,487
Derivative assets, gross amount	1,005	332
Derivative liabilities, gross amount	33	84
Derivatives designated as accounting hedges \| Interest rate contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	48,761	57,587
Derivative assets, gross amount	3	11
Derivative liabilities, gross amount	20	55
Derivatives designated as accounting hedges \| Interest rate contracts \| Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	114,600	96,900
Derivative assets, gross amount	1,002	321
Derivative liabilities, gross amount	13	29
Derivatives designated as accounting hedges \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	8,639	10,334
Derivative assets, gross amount	97	0
Derivative liabilities, gross amount	77	221
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,404	1,402
Derivative assets, gross amount	20	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	4,639	6,103
Derivative assets, gross amount	50	0
Derivative liabilities, gross amount	63	113
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	2,596	2,829
Derivative assets, gross amount	27	0
Derivative liabilities, gross amount	14	102
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	97,784	90,725
Derivative assets, gross amount	3,733	1,397
Derivative liabilities, gross amount	2,104	892
Derivatives not designated as accounting hedges \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	89,907	82,434
Derivative assets, gross amount	3,645	1,349
Derivative liabilities, gross amount	2,015	853
Derivatives not designated as accounting hedges \| Interest rate contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	68,707	62,268
Derivative assets, gross amount	1,721	552
Derivative liabilities, gross amount	224	117
Derivatives not designated as accounting hedges \| Interest rate contracts \| Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or contractual amount	6,263	6,729
Derivative assets, gross amount	87	48
Derivative liabilities, gross amount	81	30
Derivatives not designated as accounting hedges \| Foreign exchange contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	3,816	4,674
Derivative assets, gross amount	48	39
Derivative liabilities, gross amount	52	42
Derivatives not designated as accounting hedges \| Commodity contracts \| Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	17,384	15,492
Derivative assets, gross amount	1,876	758
Derivative liabilities, gross amount	1,739	694
Derivatives not designated as accounting hedges \| Other contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,614	1,562
Derivative assets, gross amount	1	0
Derivative liabilities, gross amount	$ 8	$ 9

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