Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 55,144	$ 53,314
Available for sale, gross unrealized gains	1,173	575
Available for sale, gross unrealized losses	86	74
Available-for-sale, fair value	56,231	53,815
Held to maturity, amortized cost	41,848	41,782
Investment securities held-to-maturity	43,037	42,157
Investment securities related to state and political subdivisions	870	940
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,631	3,506
Available for sale, gross unrealized gains	173	9
Available for sale, gross unrealized losses	0	28
Available-for-sale, fair value	5,804	3,487
Held to maturity, amortized cost	8,179	10,311
Held to maturity, gross unrealized gains	138	24
Held to maturity, gross unrealized losses	0	3
Investment securities held-to-maturity	8,317	10,332
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	16,118	17,599
Available for sale, gross unrealized gains	564	264
Available for sale, gross unrealized losses	6	25
Available-for-sale, fair value	16,676	17,838
Held to maturity, amortized cost	28,204	26,297
Held to maturity, gross unrealized gains	1,079	316
Held to maturity, gross unrealized losses	7	44
Investment securities held-to-maturity	29,276	26,569
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	21,749	21,105
Available for sale, gross unrealized gains	737	273
Available for sale, gross unrealized losses	6	53
Available-for-sale, fair value	22,480	21,325
Held to maturity, amortized cost	36,383	36,608
Held to maturity, gross unrealized gains	1,217	340
Held to maturity, gross unrealized losses	7	47
Investment securities held-to-maturity	37,593	36,901
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	409	532
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	7	2
Available-for-sale, fair value	404	531
Held to maturity, amortized cost	4,148	3,783
Held to maturity, gross unrealized gains	8	10
Held to maturity, gross unrealized losses	104	41
Investment securities held-to-maturity	4,052	3,752
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	90	90
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	1
Available-for-sale, fair value	90	89
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,949	1,822
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	30	3
Available-for-sale, fair value	1,919	1,820
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,448	2,444
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	37	6
Available-for-sale, fair value	2,413	2,440
Held to maturity, amortized cost	4,148	3,783
Held to maturity, gross unrealized gains	8	10
Held to maturity, gross unrealized losses	104	41
Investment securities held-to-maturity	4,052	3,752
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,714	1,978
Available for sale, gross unrealized gains	0	3
Available for sale, gross unrealized losses	8	1
Available-for-sale, fair value	1,706	1,980
Held to maturity, amortized cost	339	366
Held to maturity, gross unrealized gains	60	82
Held to maturity, gross unrealized losses	7	6
Investment securities held-to-maturity	392	442
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,906	2,179
Available for sale, gross unrealized gains	0	2
Available for sale, gross unrealized losses	15	2
Available-for-sale, fair value	1,891	2,179
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,964	12,243
Available for sale, gross unrealized gains	162	131
Available for sale, gross unrealized losses	7	1
Available-for-sale, fair value	13,119	12,373
Held to maturity, amortized cost	393	328
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	393	328
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,935	8,595
Available for sale, gross unrealized gains	135	73
Available for sale, gross unrealized losses	8	10
Available-for-sale, fair value	10,062	8,658
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	26,519	24,995
Available for sale, gross unrealized gains	297	209
Available for sale, gross unrealized losses	38	14
Available-for-sale, fair value	26,778	25,190
Held to maturity, amortized cost	732	694
Held to maturity, gross unrealized gains	60	82
Held to maturity, gross unrealized losses	7	6
Investment securities held-to-maturity	785	770
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,654	1,725
Available for sale, gross unrealized gains	73	59
Available for sale, gross unrealized losses	4	1
Available-for-sale, fair value	1,723	1,783
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	89	104
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	90	104
Held to maturity, amortized cost	585	697
Held to maturity, gross unrealized gains	28	38
Held to maturity, gross unrealized losses	6	1
Investment securities held-to-maturity	607	734
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	41,848	41,782
Held to maturity, gross unrealized gains	1,313	470
Held to maturity, gross unrealized losses	124	95
Investment securities held-to-maturity	43,037	42,157
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,685	2,941
Available for sale, gross unrealized gains	63	32
Available for sale, gross unrealized losses	1	0
Available-for-sale, fair value	2,747	2,973
Money Market Liquidity Facility
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	11,261	0
Held to maturity, gross unrealized gains	33	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	11,294	0
Total held-to-maturity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	53,109	41,782
Held to maturity, gross unrealized gains	1,346	470
Held to maturity, gross unrealized losses	124	95
Investment securities held-to-maturity	$ 54,331	42,157
Federal family education loan program
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Federal government credit support guarantee, percentage minimum	97.00%
Non-US debt securities, supranational and non US agency bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	$ 6,650	5,500
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	1,770	1,780
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	480	680
State and political subdivisions, securities in trusts
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities related to state and political subdivisions	$ 870	$ 940