Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 67,008	$ 57,897
Available for sale, gross unrealized gains	641	1,087
Available for sale, gross unrealized losses	152	26
Available-for-sale, fair value	67,497	59,048
Held to maturity, amortized cost	45,182	48,929
Investment securities held-to-maturity	45,685	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	12,893	6,453
Available for sale, gross unrealized gains	39	123
Available for sale, gross unrealized losses	28	1
Available-for-sale, fair value	12,904	6,575
Held to maturity, amortized cost	4,696	6,057
Held to maturity, gross unrealized gains	38	83
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	4,734	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	16,019	13,891
Available for sale, gross unrealized gains	251	421
Available for sale, gross unrealized losses	57	7
Available-for-sale, fair value	16,213	14,305
Held to maturity, amortized cost	33,408	36,901
Held to maturity, gross unrealized gains	585	955
Held to maturity, gross unrealized losses	259	67
Investment securities held-to-maturity	33,734	37,789
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	28,912	20,344
Available for sale, gross unrealized gains	290	544
Available for sale, gross unrealized losses	85	8
Available-for-sale, fair value	29,117	20,880
Held to maturity, amortized cost	38,104	42,958
Held to maturity, gross unrealized gains	623	1,038
Held to maturity, gross unrealized losses	259	67
Investment securities held-to-maturity	38,468	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	1,989	1,994
Available for sale, gross unrealized gains	13	4
Available for sale, gross unrealized losses	0	2
Available-for-sale, fair value	2,002	1,996
Held to maturity, amortized cost	233	303
Held to maturity, gross unrealized gains	69	68
Held to maturity, gross unrealized losses	2	4
Investment securities held-to-maturity	300	367
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,451	2,294
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	2	4
Available-for-sale, fair value	2,451	2,291
Foreign sovereign, supranational and non-U.S. agency
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,561	21,769
Available for sale, gross unrealized gains	171	321
Available for sale, gross unrealized losses	42	3
Available-for-sale, fair value	20,690	22,087
Held to maturity, amortized cost	1,595	342
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	1	0
Investment securities held-to-maturity	1,594	342
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,414	3,297
Available for sale, gross unrealized gains	35	58
Available for sale, gross unrealized losses	17	0
Available-for-sale, fair value	3,432	3,355
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	28,415	29,354
Available for sale, gross unrealized gains	221	384
Available for sale, gross unrealized losses	61	9
Available-for-sale, fair value	28,575	29,729
Held to maturity, amortized cost	1,828	645
Held to maturity, gross unrealized gains	69	68
Held to maturity, gross unrealized losses	3	4
Investment securities held-to-maturity	1,894	709
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	253	313
Available for sale, gross unrealized gains	5	2
Available for sale, gross unrealized losses	0	1
Available-for-sale, fair value	258	314
Held to maturity, amortized cost	4,860	4,774
Held to maturity, gross unrealized gains	54	33
Held to maturity, gross unrealized losses	13	25
Investment securities held-to-maturity	4,901	4,782
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,690	2,969
Available for sale, gross unrealized gains	5	3
Available for sale, gross unrealized losses	1	6
Available-for-sale, fair value	4,694	2,966
Non-agency CMBS and RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	64	76
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	65	78
Held to maturity, amortized cost	392	554
Held to maturity, gross unrealized gains	31	30
Held to maturity, gross unrealized losses	1	1
Investment securities held-to-maturity	422	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	5,097	3,358
Available for sale, gross unrealized gains	13	7
Available for sale, gross unrealized losses	1	7
Available-for-sale, fair value	5,109	3,448
Held to maturity, amortized cost	5,252	5,328
Held to maturity, gross unrealized gains	85	63
Held to maturity, gross unrealized losses	14	26
Investment securities held-to-maturity	5,323	5,365
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,423	1,470
Available for sale, gross unrealized gains	70	80
Available for sale, gross unrealized losses	2	2
Available-for-sale, fair value	1,491	1,548
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,161	3,371
Available for sale, gross unrealized gains	47	72
Available for sale, gross unrealized losses	3	0
Available-for-sale, fair value	3,205	3,443
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	45,184	48,931
Held to maturity, gross unrealized gains	777	1,169
Held to maturity, gross unrealized losses	276	97
Investment securities held-to-maturity	45,685	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	45,184	52,231
Held to maturity, gross unrealized gains	777	1,173
Held to maturity, gross unrealized losses	276	97
Investment securities held-to-maturity	45,685	53,307
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 1,940	1,880
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	$ 690	700
US debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,200	3,440
Non-agency CMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	319	464
Non-agency RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	$ 73	$ 90