Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Notional or contractual amount	$ 245,407	$ 232,327
Derivative assets, gross amount	4,904	3,415
Derivative liabilities, gross amount	3,463	1,518
Derivative asset, netting adjustments	(975)	(1,148)
Derivative liability, netting adjustments	(904)	(739)
Total derivative assets	3,929	2,267
Total derivative liabilities	2,559	779
Net valuation allowance on derivative assets and liabilities for non-performance risk	17	31
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	143,514	138,724
Derivative assets, gross amount	657	921
Derivative liabilities, gross amount	56	368
Derivatives designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	134,463	129,499
Derivative assets, gross amount	474	757
Derivative liabilities, gross amount	20	11
Derivatives designated as accounting hedges | Interest rate contracts | Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	44,563	47,349
Derivative assets, gross amount	29	9
Derivative liabilities, gross amount	10	10
Derivatives designated as accounting hedges | Interest rate contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	89,900	82,150
Derivative assets, gross amount	445	748
Derivative liabilities, gross amount	10	1
Derivatives designated as accounting hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	9,051	9,225
Derivative assets, gross amount	183	164
Derivative liabilities, gross amount	36	357
Derivatives designated as accounting hedges | Foreign exchange contracts | Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,448	1,527
Derivative assets, gross amount	46	164
Derivative liabilities, gross amount	0	0
Derivatives designated as accounting hedges | Foreign exchange contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	4,278	4,582
Derivative assets, gross amount	87	0
Derivative liabilities, gross amount	2	161
Derivatives designated as accounting hedges | Foreign exchange contracts | Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	3,325	3,116
Derivative assets, gross amount	50	0
Derivative liabilities, gross amount	34	196
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	101,893	93,603
Derivative assets, gross amount	4,247	2,494
Derivative liabilities, gross amount	3,407	1,150
Derivatives not designated as accounting hedges | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	97,254	90,007
Derivative assets, gross amount	4,203	2,422
Derivative liabilities, gross amount	3,377	1,088
Derivatives not designated as accounting hedges | Interest rate contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	71,622	68,459
Derivative assets, gross amount	848	1,429
Derivative liabilities, gross amount	202	198
Derivatives not designated as accounting hedges | Interest rate contracts | Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or contractual amount	2,656	1,770
Derivative assets, gross amount	42	71
Derivative liabilities, gross amount	27	56
Derivatives not designated as accounting hedges | Foreign exchange contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	4,077	4,677
Derivative assets, gross amount	53	58
Derivative liabilities, gross amount	39	70
Derivatives not designated as accounting hedges | Commodity contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	21,555	16,871
Derivative assets, gross amount	3,302	935
Derivative liabilities, gross amount	3,136	820
Derivatives not designated as accounting hedges | Other contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,983	1,826
Derivative assets, gross amount	2	1
Derivative liabilities, gross amount	$ 3	$ 6