Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 60,713	$ 53,314
Available for sale, gross unrealized gains	1,113	575
Available for sale, gross unrealized losses	46	74
Available-for-sale, fair value	61,780	53,815
Held to maturity, amortized cost	45,394	41,782
Investment securities held-to-maturity	46,510	42,157
Investment securities related to state and political subdivisions	850	940
Debt securities, held-to-maturity, allowance for credit loss	3
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,128	3,506
Available for sale, gross unrealized gains	165	9
Available for sale, gross unrealized losses	0	28
Available-for-sale, fair value	7,293	3,487
Held to maturity, amortized cost	6,668	10,311
Held to maturity, gross unrealized gains	110	24
Held to maturity, gross unrealized losses	0	3
Investment securities held-to-maturity	6,778	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	17,754	17,599
Available for sale, gross unrealized gains	464	264
Available for sale, gross unrealized losses	7	25
Available-for-sale, fair value	18,211	17,838
Held to maturity, amortized cost	33,096	26,297
Held to maturity, gross unrealized gains	1,001	316
Held to maturity, gross unrealized losses	43	44
Investment securities held-to-maturity	34,054	26,569
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	24,882	21,105
Available for sale, gross unrealized gains	629	273
Available for sale, gross unrealized losses	7	53
Available-for-sale, fair value	25,504	21,325
Held to maturity, amortized cost	39,764	36,608
Held to maturity, gross unrealized gains	1,111	340
Held to maturity, gross unrealized losses	43	47
Investment securities held-to-maturity	40,832	36,901
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	356	532
Available for sale, gross unrealized gains	3	1
Available for sale, gross unrealized losses	2	2
Available-for-sale, fair value	357	531
Held to maturity, amortized cost	4,323	3,783
Held to maturity, gross unrealized gains	16	10
Held to maturity, gross unrealized losses	53	41
Investment securities held-to-maturity	4,286	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	2,553	1,822
Available for sale, gross unrealized gains	1	1
Available for sale, gross unrealized losses	16	3
Available-for-sale, fair value	2,538	1,820
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,999	2,444
Available for sale, gross unrealized gains	4	2
Available for sale, gross unrealized losses	18	6
Available-for-sale, fair value	2,985	2,440
Held to maturity, amortized cost	4,323	3,783
Held to maturity, gross unrealized gains	16	10
Held to maturity, gross unrealized losses	53	41
Investment securities held-to-maturity	4,286	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	1,865	1,978
Available for sale, gross unrealized gains	2	3
Available for sale, gross unrealized losses	4	1
Available-for-sale, fair value	1,863	1,980
Held to maturity, amortized cost	321	366
Held to maturity, gross unrealized gains	63	82
Held to maturity, gross unrealized losses	6	6
Investment securities held-to-maturity	378	442
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,037	2,179
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	7	2
Available-for-sale, fair value	2,031	2,179
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,670	12,243
Available for sale, gross unrealized gains	180	131
Available for sale, gross unrealized losses	1	1
Available-for-sale, fair value	12,849	12,373
Held to maturity, amortized cost	419	328
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	419	328
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	11,162	8,595
Available for sale, gross unrealized gains	153	73
Available for sale, gross unrealized losses	5	10
Available-for-sale, fair value	11,310	8,658
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	27,734	24,995
Available for sale, gross unrealized gains	336	209
Available for sale, gross unrealized losses	17	14
Available-for-sale, fair value	28,053	25,190
Held to maturity, amortized cost	740	694
Held to maturity, gross unrealized gains	63	82
Held to maturity, gross unrealized losses	6	6
Investment securities held-to-maturity	797	770
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,620	1,725
Available for sale, gross unrealized gains	76	59
Available for sale, gross unrealized losses	2	1
Available-for-sale, fair value	1,694	1,783
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	83	104
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	84	104
Held to maturity, amortized cost	569	697
Held to maturity, gross unrealized gains	29	38
Held to maturity, gross unrealized losses	3	1
Investment securities held-to-maturity	595	734
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	45,396	41,782
Held to maturity, gross unrealized gains	1,219	470
Held to maturity, gross unrealized losses	105	95
Investment securities held-to-maturity	46,510	42,157
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,395	2,941
Available for sale, gross unrealized gains	67	32
Available for sale, gross unrealized losses	2	0
Available-for-sale, fair value	3,460	2,973
Money Market Liquidity Facility
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	4,825	0
Held to maturity, gross unrealized gains	16	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	4,841	0
Total held-to-maturity securities(4)(5)
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	50,221	41,782
Held to maturity, gross unrealized gains	1,235	470
Held to maturity, gross unrealized losses	105	95
Investment securities held-to-maturity	$ 51,351	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	$ 7,250	5,500
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	2,010	1,780
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	$ 450	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		$ 940