Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 69,907	$ 57,987
Available for sale, gross unrealized gains	550	1,087
Available for sale, gross unrealized losses	178	26
Available-for-sale, fair value	70,279	59,048
Held to maturity, amortized cost	43,346	48,929
Investment securities held-to-maturity	43,728	50,003
Debt securities, held-to-maturity, allowance for credit loss	2
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	14,372	6,453
Available for sale, gross unrealized gains	30	123
Available for sale, gross unrealized losses	63	1
Available-for-sale, fair value	14,339	6,575
Held to maturity, amortized cost	2,709	6,057
Held to maturity, gross unrealized gains	22	83
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	2,731	6,140
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	16,051	13,891
Available for sale, gross unrealized gains	215	421
Available for sale, gross unrealized losses	43	7
Available-for-sale, fair value	16,223	14,305
Held to maturity, amortized cost	33,525	36,901
Held to maturity, gross unrealized gains	525	955
Held to maturity, gross unrealized losses	309	67
Investment securities held-to-maturity	33,741	37,789
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	30,423	20,344
Available for sale, gross unrealized gains	245	544
Available for sale, gross unrealized losses	106	8
Available-for-sale, fair value	30,562	20,880
Held to maturity, amortized cost	36,234	42,958
Held to maturity, gross unrealized gains	547	1,038
Held to maturity, gross unrealized losses	309	67
Investment securities held-to-maturity	36,472	43,929
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,130	1,994
Available for sale, gross unrealized gains	12	4
Available for sale, gross unrealized losses	1	2
Available-for-sale, fair value	2,141	1,996
Held to maturity, amortized cost	209	303
Held to maturity, gross unrealized gains	65	68
Held to maturity, gross unrealized losses	2	4
Investment securities held-to-maturity	272	367
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,365	2,294
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	2	4
Available-for-sale, fair value	2,365	2,291
Non-U.S. sovereign, supranational and non-U.S. agency
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,747	21,769
Available for sale, gross unrealized gains	150	321
Available for sale, gross unrealized losses	43	3
Available-for-sale, fair value	22,854	22,087
Held to maturity, amortized cost	1,508	342
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	3	0
Investment securities held-to-maturity	1,505	342
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,294	3,297
Available for sale, gross unrealized gains	29	58
Available for sale, gross unrealized losses	17	0
Available-for-sale, fair value	3,306	3,355
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	30,536	29,354
Available for sale, gross unrealized gains	193	384
Available for sale, gross unrealized losses	63	9
Available-for-sale, fair value	30,666	29,729
Held to maturity, amortized cost	1,717	645
Held to maturity, gross unrealized gains	65	68
Held to maturity, gross unrealized losses	5	4
Investment securities held-to-maturity	1,777	709
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	228	313
Available for sale, gross unrealized gains	3	2
Available for sale, gross unrealized losses	0	1
Available-for-sale, fair value	231	314
Held to maturity, amortized cost	5,017	4,774
Held to maturity, gross unrealized gains	64	33
Held to maturity, gross unrealized losses	13	25
Investment securities held-to-maturity	5,068	4,782
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,293	2,969
Available for sale, gross unrealized gains	4	3
Available for sale, gross unrealized losses	1	6
Available-for-sale, fair value	4,296	2,966
Non-agency CMBS and RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	58	76
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	59	78
Held to maturity, amortized cost	380	554
Held to maturity, gross unrealized gains	31	30
Held to maturity, gross unrealized losses	0	1
Investment securities held-to-maturity	411	583
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	90	90
Available for sale, gross unrealized gains	2	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	92	90
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,669	3,448
Available for sale, gross unrealized gains	10	7
Available for sale, gross unrealized losses	1	7
Available-for-sale, fair value	4,678	3,448
Held to maturity, amortized cost	5,397	5,328
Held to maturity, gross unrealized gains	95	63
Held to maturity, gross unrealized losses	13	26
Investment securities held-to-maturity	5,479	5,365
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,336	1,470
Available for sale, gross unrealized gains	63	80
Available for sale, gross unrealized losses	3	2
Available-for-sale, fair value	1,396	1,548
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,943	3,371
Available for sale, gross unrealized gains	39	72
Available for sale, gross unrealized losses	5	0
Available-for-sale, fair value	2,977	3,443
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	43,348	48,931
Held to maturity, gross unrealized gains	707	1,169
Held to maturity, gross unrealized losses	327	97
Investment securities held-to-maturity	43,728	50,003
Held-to-maturity under money market mutual fund liquidity facility
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	0	3,300
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	0	3,304
Including MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	43,348	52,231
Held to maturity, gross unrealized gains	707	1,173
Held to maturity, gross unrealized losses	327	97
Investment securities held-to-maturity	43,728	53,307
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,760	1,880
Non-US Collateralized Loan Obiligations [Member]
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 880	960
Federal family education loan program
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Federal government credit support guarantee, percentage minimum	97.00%
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	$ 610	700
US debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,980	3,440
Non-agency CMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	315	464
Non-agency RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	$ 65	$ 90