Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 53,314	$ 45,359
Available for sale, gross unrealized gains	575	107
Available for sale, gross unrealized losses	74	318
Available-for-sale, fair value	53,815	45,148
Held to maturity, amortized cost	41,782	41,914
Held to maturity, gross unrealized gains	470	175
Held to maturity, gross unrealized losses	95	738
Investment securities held-to-maturity	42,157	41,351
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,506	1,035
Available for sale, gross unrealized gains	9	4
Available for sale, gross unrealized losses	28	0
Available-for-sale, fair value	3,487	1,039
Held to maturity, amortized cost	10,311	14,794
Held to maturity, gross unrealized gains	24	0
Held to maturity, gross unrealized losses	3	199
Investment securities held-to-maturity	10,332	14,595
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	17,599	16,112
Available for sale, gross unrealized gains	264	37
Available for sale, gross unrealized losses	25	181
Available-for-sale, fair value	17,838	15,968
Held to maturity, amortized cost	26,297	21,647
Held to maturity, gross unrealized gains	316	24
Held to maturity, gross unrealized losses	44	518
Investment securities held-to-maturity	26,569	21,153
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	21,105	17,147
Available for sale, gross unrealized gains	273	41
Available for sale, gross unrealized losses	53	181
Available-for-sale, fair value	21,325	17,007
Held to maturity, amortized cost	36,608	36,441
Held to maturity, gross unrealized gains	340	24
Held to maturity, gross unrealized losses	47	717
Investment securities held-to-maturity	36,901	35,748
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	532	538
Available for sale, gross unrealized gains	1	4
Available for sale, gross unrealized losses	2	1
Available-for-sale, fair value	531	541
Held to maturity, amortized cost	3,783	3,191
Held to maturity, gross unrealized gains	10	35
Held to maturity, gross unrealized losses	41	10
Investment securities held-to-maturity	3,752	3,216
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	90	609
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	1	26
Available-for-sale, fair value	89	583
Held to maturity, amortized cost	0	193
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	0	193
Asset-backed securities, collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,822	594
Available for sale, gross unrealized gains	1	1
Available for sale, gross unrealized losses	3	2
Available-for-sale, fair value	1,820	593
Held to maturity, amortized cost	0	1
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	0	1
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,444	1,741
Available for sale, gross unrealized gains	2	5
Available for sale, gross unrealized losses	6	29
Available-for-sale, fair value	2,440	1,717
Held to maturity, amortized cost	3,783	3,385
Held to maturity, gross unrealized gains	10	35
Held to maturity, gross unrealized losses	41	10
Investment securities held-to-maturity	3,752	3,410
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,978	1,687
Available for sale, gross unrealized gains	3	0
Available for sale, gross unrealized losses	1	5
Available-for-sale, fair value	1,980	1,682
Held to maturity, amortized cost	366	638
Held to maturity, gross unrealized gains	82	77
Held to maturity, gross unrealized losses	6	9
Investment securities held-to-maturity	442	706
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,179	1,580
Available for sale, gross unrealized gains	2	0
Available for sale, gross unrealized losses	2	6
Available-for-sale, fair value	2,179	1,574
Held to maturity, amortized cost	0	223
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	0	223
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,243	12,816
Available for sale, gross unrealized gains	131	22
Available for sale, gross unrealized losses	1	45
Available-for-sale, fair value	12,373	12,793
Held to maturity, amortized cost	328	358
Held to maturity, gross unrealized gains	0	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	328	359
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,595	6,600
Available for sale, gross unrealized gains	73	18
Available for sale, gross unrealized losses	10	16
Available-for-sale, fair value	8,658	6,602
Held to maturity, amortized cost	0	46
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	0	46
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	24,995	22,683
Available for sale, gross unrealized gains	209	40
Available for sale, gross unrealized losses	14	72
Available-for-sale, fair value	25,190	22,651
Held to maturity, amortized cost	694	1,265
Held to maturity, gross unrealized gains	82	78
Held to maturity, gross unrealized losses	6	9
Investment securities held-to-maturity	770	1,334
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,725	1,905
Available for sale, gross unrealized gains	59	20
Available for sale, gross unrealized losses	1	7
Available-for-sale, fair value	1,783	1,918
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	104	200
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	3
Available-for-sale, fair value	104	197
Held to maturity, amortized cost	697	823
Held to maturity, gross unrealized gains	38	38
Held to maturity, gross unrealized losses	1	2
Investment securities held-to-maturity	734	859
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,941	1,683
Available for sale, gross unrealized gains	32	1
Available for sale, gross unrealized losses	0	26
Available-for-sale, fair value	$ 2,973	1,658
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	$ 5,500	3,200
Non-U.S. debt securities, corporate bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	1,780	1,330
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available-for-sale, fair value	680	1,300
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	$ 1,050

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