Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 59,979	$ 57,987
Available for sale, gross unrealized gains	749	1,087
Available for sale, gross unrealized losses	216	26
Available-for-sale, fair value	60,512	59,048
Held to maturity, amortized cost	46,261	48,929
Investment securities held-to-maturity	46,752	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	8,948	6,453
Available for sale, gross unrealized gains	28	123
Available for sale, gross unrealized losses	39	1
Available-for-sale, fair value	8,937	6,575
Held to maturity, amortized cost	5,530	6,057
Held to maturity, gross unrealized gains	61	83
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	5,591	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	14,181	13,891
Available for sale, gross unrealized gains	326	421
Available for sale, gross unrealized losses	82	7
Available-for-sale, fair value	14,425	14,305
Held to maturity, amortized cost	34,930	36,901
Held to maturity, gross unrealized gains	629	955
Held to maturity, gross unrealized losses	322	67
Investment securities held-to-maturity	35,237	37,789
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	23,129	20,344
Available for sale, gross unrealized gains	354	544
Available for sale, gross unrealized losses	121	8
Available-for-sale, fair value	23,362	20,880
Held to maturity, amortized cost	40,460	42,958
Held to maturity, gross unrealized gains	690	1,038
Held to maturity, gross unrealized losses	322	67
Investment securities held-to-maturity	40,828	43,929
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	283	313
Available for sale, gross unrealized gains	5	2
Available for sale, gross unrealized losses	0	1
Available-for-sale, fair value	288	314
Held to maturity, amortized cost	4,745	4,774
Held to maturity, gross unrealized gains	43	33
Held to maturity, gross unrealized losses	20	25
Investment securities held-to-maturity	4,768	4,782
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	1	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	91	90
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,770	2,969
Available for sale, gross unrealized gains	6	3
Available for sale, gross unrealized losses	1	6
Available-for-sale, fair value	3,775	2,966
Non-agency CMBS and RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	70	76
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	71	78
Held to maturity, amortized cost	526	554
Held to maturity, gross unrealized gains	32	30
Held to maturity, gross unrealized losses	1	1
Investment securities held-to-maturity	557	583
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,213	3,448
Available for sale, gross unrealized gains	13	7
Available for sale, gross unrealized losses	1	7
Available-for-sale, fair value	4,225	3,448
Held to maturity, amortized cost	5,271	5,328
Held to maturity, gross unrealized gains	75	63
Held to maturity, gross unrealized losses	21	26
Investment securities held-to-maturity	5,325	5,365
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,021	1,994
Available for sale, gross unrealized gains	11	4
Available for sale, gross unrealized losses	0	2
Available-for-sale, fair value	2,032	1,996
Held to maturity, amortized cost	286	303
Held to maturity, gross unrealized gains	70	68
Held to maturity, gross unrealized losses	3	4
Investment securities held-to-maturity	353	367
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,296	2,294
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	1	4
Available-for-sale, fair value	2,297	2,291
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,773	12,337
Available for sale, gross unrealized gains	138	202
Available for sale, gross unrealized losses	1	0
Available-for-sale, fair value	9,910	12,539
Held to maturity, amortized cost	246	342
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	246	342
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	13,679	12,729
Available for sale, gross unrealized gains	111	177
Available for sale, gross unrealized losses	81	3
Available-for-sale, fair value	13,709	12,903
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	27,769	29,354
Available for sale, gross unrealized gains	262	384
Available for sale, gross unrealized losses	83	9
Available-for-sale, fair value	27,948	29,729
Held to maturity, amortized cost	532	645
Held to maturity, gross unrealized gains	70	68
Held to maturity, gross unrealized losses	3	4
Investment securities held-to-maturity	599	709
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,431	1,470
Available for sale, gross unrealized gains	69	80
Available for sale, gross unrealized losses	2	2
Available-for-sale, fair value	1,498	1,548
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,437	3,371
Available for sale, gross unrealized gains	51	72
Available for sale, gross unrealized losses	9	0
Available-for-sale, fair value	3,479	3,443
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	46,263	48,931
Held to maturity, gross unrealized gains	835	1,169
Held to maturity, gross unrealized losses	346	97
Investment securities held-to-maturity	46,752	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	201	3,300
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	201	3,304
Including MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	46,464	52,231
Held to maturity, gross unrealized gains	835	1,173
Held to maturity, gross unrealized losses	346	97
Investment securities held-to-maturity	$ 46,953	53,307
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	$ 10,130	9,550
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	1,900	1,880
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	430	470
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	700	700
Non-Agency CMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	446	464
Non-Agency RMBS
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	$ 80	$ 90