Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 57,987	$ 53,314
Available for sale, gross unrealized gains	1,087	575
Available for sale, gross unrealized losses	26	74
Available-for-sale, fair value	59,048	53,815
Held to maturity, amortized cost	48,929	41,782
Investment securities held-to-maturity	50,003	42,157
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	6,453	3,506
Available for sale, gross unrealized gains	123	9
Available for sale, gross unrealized losses	1	28
Available-for-sale, fair value	6,575	3,487
Held to maturity, amortized cost	6,057	10,311
Held to maturity, gross unrealized gains	83	24
Held to maturity, gross unrealized losses	0	3
Investment securities held-to-maturity	6,140	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	13,891	17,599
Available for sale, gross unrealized gains	421	264
Available for sale, gross unrealized losses	7	25
Available-for-sale, fair value	14,305	17,838
Held to maturity, amortized cost	36,883	26,297
Held to maturity, gross unrealized gains	955	316
Held to maturity, gross unrealized losses	67	44
Investment securities held-to-maturity	37,771	26,569
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,344	21,105
Available for sale, gross unrealized gains	544	273
Available for sale, gross unrealized losses	8	53
Available-for-sale, fair value	20,880	21,325
Held to maturity, amortized cost	42,940	36,608
Held to maturity, gross unrealized gains	1,038	340
Held to maturity, gross unrealized losses	67	47
Investment securities held-to-maturity	43,911	36,901
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	313	532
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	1	2
Available-for-sale, fair value	314	531
Held to maturity, amortized cost	4,774	3,783
Held to maturity, gross unrealized gains	33	10
Held to maturity, gross unrealized losses	25	41
Investment securities held-to-maturity	4,782	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	2,969	1,822
Available for sale, gross unrealized gains	3	1
Available for sale, gross unrealized losses	6	3
Available-for-sale, fair value	2,966	1,820
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,372	2,444
Available for sale, gross unrealized gains	5	2
Available for sale, gross unrealized losses	7	6
Available-for-sale, fair value	3,370	2,440
Held to maturity, amortized cost	4,774	3,783
Held to maturity, gross unrealized gains	33	10
Held to maturity, gross unrealized losses	25	41
Investment securities held-to-maturity	4,782	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	1,994	1,978
Available for sale, gross unrealized gains	4	3
Available for sale, gross unrealized losses	2	1
Available-for-sale, fair value	1,996	1,980
Held to maturity, amortized cost	303	366
Held to maturity, gross unrealized gains	68	82
Held to maturity, gross unrealized losses	4	6
Investment securities held-to-maturity	367	442
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,294	2,179
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	4	2
Available-for-sale, fair value	2,291	2,179
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,337	12,243
Available for sale, gross unrealized gains	202	131
Available for sale, gross unrealized losses	0	1
Available-for-sale, fair value	12,539	12,373
Held to maturity, amortized cost	342	328
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	342	328
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,729	8,595
Available for sale, gross unrealized gains	177	73
Available for sale, gross unrealized losses	3	10
Available-for-sale, fair value	12,903	8,658
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	29,354	24,995
Available for sale, gross unrealized gains	384	209
Available for sale, gross unrealized losses	9	14
Available-for-sale, fair value	29,729	25,190
Held to maturity, amortized cost	645	694
Held to maturity, gross unrealized gains	68	82
Held to maturity, gross unrealized losses	4	6
Investment securities held-to-maturity	709	770
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,470	1,725
Available for sale, gross unrealized gains	80	59
Available for sale, gross unrealized losses	2	1
Available-for-sale, fair value	1,548	1,783
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	76	104
Available for sale, gross unrealized gains	2	0
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	78	104
Held to maturity, amortized cost	572	697
Held to maturity, gross unrealized gains	30	38
Held to maturity, gross unrealized losses	1	1
Investment securities held-to-maturity	601	734
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,371	2,941
Available for sale, gross unrealized gains	72	32
Available for sale, gross unrealized losses	0	0
Available-for-sale, fair value	$ 3,443	2,973
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	$ 9,550	5,500
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	1,880	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	700	940
Total Before MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	48,931	41,782
Held to maturity, gross unrealized gains	1,169	470
Held to maturity, gross unrealized losses	97	95
Investment securities held-to-maturity	50,003	42,157
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	3,300	0
Held to maturity, gross unrealized gains	4	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	3,304	0
Including MMLF
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Held to maturity, amortized cost	52,231	41,782
Held to maturity, gross unrealized gains	1,173	470
Held to maturity, gross unrealized losses	97	95
Investment securities held-to-maturity	$ 53,307	$ 42,157