Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 52,736	$ 45,359
Available for sale, gross unrealized gains	579	107
Available for sale, gross unrealized losses	73	318
Investment securities available-for-sale	53,242	45,148
Held to maturity, amortized cost	39,236	41,914
Held to maturity, gross unrealized gains	345	175
Held to maturity, gross unrealized losses	108	738
Investment securities held-to-maturity	39,473	41,351
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,035	1,035
Available for sale, gross unrealized gains	10	4
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	1,045	1,039
Held to maturity, amortized cost	12,433	14,794
Held to maturity, gross unrealized gains	10	0
Held to maturity, gross unrealized losses	24	199
Investment securities held-to-maturity	12,419	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	21,050	16,112
Available for sale, gross unrealized gains	226	37
Available for sale, gross unrealized losses	43	181
Investment securities available-for-sale	21,233	15,968
Held to maturity, amortized cost	21,466	21,647
Held to maturity, gross unrealized gains	190	24
Held to maturity, gross unrealized losses	52	518
Investment securities held-to-maturity	21,604	21,153
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,085	17,147
Available for sale, gross unrealized gains	236	41
Available for sale, gross unrealized losses	43	181
Investment securities available-for-sale	22,278	17,007
Held to maturity, amortized cost	33,899	36,441
Held to maturity, gross unrealized gains	200	24
Held to maturity, gross unrealized losses	76	717
Investment securities held-to-maturity	34,023	35,748
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	596	538
Available for sale, gross unrealized gains	3	4
Available for sale, gross unrealized losses	1	1
Investment securities available-for-sale	598	541
Held to maturity, amortized cost	3,603	3,191
Held to maturity, gross unrealized gains	20	35
Held to maturity, gross unrealized losses	23	10
Investment securities held-to-maturity	3,600	3,216
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	251	609
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	11	26
Investment securities available-for-sale	240	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	1,454	594
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	2	2
Investment securities available-for-sale	1,452	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	2,301	1,741
Available for sale, gross unrealized gains	3	5
Available for sale, gross unrealized losses	14	29
Investment securities available-for-sale	2,290	1,717
Held to maturity, amortized cost	3,603	3,385
Held to maturity, gross unrealized gains	20	35
Held to maturity, gross unrealized losses	23	10
Investment securities held-to-maturity	3,600	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	1,872	1,687
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	3	5
Investment securities available-for-sale	1,870	1,682
Held to maturity, amortized cost	501	638
Held to maturity, gross unrealized gains	84	77
Held to maturity, gross unrealized losses	8	9
Investment securities held-to-maturity	577	706
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,656	1,580
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	2	6
Investment securities available-for-sale	1,655	1,574
Held to maturity, amortized cost	95	223
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	95	223
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	13,662	12,816
Available for sale, gross unrealized gains	162	22
Available for sale, gross unrealized losses	6	45
Investment securities available-for-sale	13,818	12,793
Held to maturity, amortized cost	362	358
Held to maturity, gross unrealized gains	1	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	363	359
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,010	6,600
Available for sale, gross unrealized gains	96	18
Available for sale, gross unrealized losses	2	16
Investment securities available-for-sale	7,104	6,602
Held to maturity, amortized cost	1	46
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	1	46
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	24,200	22,683
Available for sale, gross unrealized gains	260	40
Available for sale, gross unrealized losses	13	72
Investment securities available-for-sale	24,447	22,651
Held to maturity, amortized cost	959	1,265
Held to maturity, gross unrealized gains	85	78
Held to maturity, gross unrealized losses	8	9
Investment securities held-to-maturity	1,036	1,334
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,852	1,905
Available for sale, gross unrealized gains	52	20
Available for sale, gross unrealized losses	2	7
Investment securities available-for-sale	1,902	1,918
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	122	200
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	3
Investment securities available-for-sale	122	197
Held to maturity, amortized cost	775	823
Held to maturity, gross unrealized gains	40	38
Held to maturity, gross unrealized losses	1	2
Investment securities held-to-maturity	814	859
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,176	1,683
Available for sale, gross unrealized gains	28	1
Available for sale, gross unrealized losses	1	26
Investment securities available-for-sale	$ 2,203	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, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 920	1,300
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	1,440	1,330
US States and Political Subdivisions Debt Securities - Trusts
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 1,060	$ 1,050