Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 55,199	$ 53,314
Available for sale, gross unrealized gains	951	575
Available for sale, gross unrealized losses	307	74
Available-for-sale, fair value	55,843	53,815
Held to maturity, amortized cost	41,150	41,782
Investment securities held-to-maturity	42,201	42,157
Investment securities related to state and political subdivisions	930	940
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,983	3,506
Available for sale, gross unrealized gains	167	9
Available for sale, gross unrealized losses	0	28
Available-for-sale, fair value	5,150	3,487
Held to maturity, amortized cost	9,268	10,311
Held to maturity, gross unrealized gains	171	24
Held to maturity, gross unrealized losses	0	3
Investment securities held-to-maturity	9,439	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	17,842	17,599
Available for sale, gross unrealized gains	547	264
Available for sale, gross unrealized losses	25	25
Available-for-sale, fair value	18,364	17,838
Held to maturity, amortized cost	26,613	26,297
Held to maturity, gross unrealized gains	970	316
Held to maturity, gross unrealized losses	7	44
Investment securities held-to-maturity	27,576	26,569
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,825	21,105
Available for sale, gross unrealized gains	714	273
Available for sale, gross unrealized losses	25	53
Available-for-sale, fair value	23,514	21,325
Held to maturity, amortized cost	35,881	36,608
Held to maturity, gross unrealized gains	1,141	340
Held to maturity, gross unrealized losses	7	47
Investment securities held-to-maturity	37,015	36,901
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	466	532
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	12	2
Available-for-sale, fair value	454	531
Held to maturity, amortized cost	4,055	3,783
Held to maturity, gross unrealized gains	1	10
Held to maturity, gross unrealized losses	148	41
Investment securities held-to-maturity	3,908	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	5	1
Available-for-sale, fair value	85	89
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,931	1,822
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	90	3
Available-for-sale, fair value	1,841	1,820
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,487	2,444
Available for sale, gross unrealized gains	0	2
Available for sale, gross unrealized losses	107	6
Available-for-sale, fair value	2,380	2,440
Held to maturity, amortized cost	4,055	3,783
Held to maturity, gross unrealized gains	1	10
Held to maturity, gross unrealized losses	148	41
Investment securities held-to-maturity	3,908	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	1,710	1,978
Available for sale, gross unrealized gains	0	3
Available for sale, gross unrealized losses	18	1
Available-for-sale, fair value	1,692	1,980
Held to maturity, amortized cost	335	366
Held to maturity, gross unrealized gains	56	82
Held to maturity, gross unrealized losses	14	6
Investment securities held-to-maturity	377	442
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,907	2,179
Available for sale, gross unrealized gains	0	2
Available for sale, gross unrealized losses	52	2
Available-for-sale, fair value	1,855	2,179
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,952	12,243
Available for sale, gross unrealized gains	121	131
Available for sale, gross unrealized losses	18	1
Available-for-sale, fair value	13,055	12,373
Held to maturity, amortized cost	279	328
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	280	328
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,761	8,595
Available for sale, gross unrealized gains	59	73
Available for sale, gross unrealized losses	46	10
Available-for-sale, fair value	8,774	8,658
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	25,330	24,995
Available for sale, gross unrealized gains	180	209
Available for sale, gross unrealized losses	134	14
Available-for-sale, fair value	25,376	25,190
Held to maturity, amortized cost	614	694
Held to maturity, gross unrealized gains	57	82
Held to maturity, gross unrealized losses	14	6
Investment securities held-to-maturity	657	770
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,724	1,725
Available for sale, gross unrealized gains	48	59
Available for sale, gross unrealized losses	7	1
Available-for-sale, fair value	1,765	1,783
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	96	104
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	96	104
Held to maturity, amortized cost	600	697
Held to maturity, gross unrealized gains	28	38
Held to maturity, gross unrealized losses	7	1
Investment securities held-to-maturity	621	734
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	41,150	41,782
Held to maturity, gross unrealized gains	1,227	470
Held to maturity, gross unrealized losses	176	95
Investment securities held-to-maturity	42,201	42,157
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,737	2,941
Available for sale, gross unrealized gains	9	32
Available for sale, gross unrealized losses	34	0
Available-for-sale, fair value	2,712	2,973
Money Market Liquidity Facility
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	26,812	0
Held to maturity, gross unrealized gains	9	0
Held to maturity, gross unrealized losses	13	0
Investment securities held-to-maturity	26,808	0
Total held-to-maturity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	67,962	41,782
Held to maturity, gross unrealized gains	1,236	470
Held to maturity, gross unrealized losses	189	95
Investment securities held-to-maturity	$ 69,009	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	$ 6,000	5,500
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	1,710	1,780
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	470	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	$ 930	$ 940