Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 48,827	$ 45,359
Available for sale, gross unrealized gains	350	107
Available for sale, gross unrealized losses	175	318
Investment securities available-for-sale	49,002	45,148
Held to maturity, amortized cost	41,145	41,914
Held to maturity, gross unrealized gains	225	175
Held to maturity, gross unrealized losses	399	738
Investment securities held-to-maturity	40,971	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	6	4
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	1,041	1,039
Held to maturity, amortized cost	13,369	14,794
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	123	199
Investment securities held-to-maturity	13,246	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	20,020	16,112
Available for sale, gross unrealized gains	132	37
Available for sale, gross unrealized losses	109	181
Investment securities available-for-sale	20,043	15,968
Held to maturity, amortized cost	22,568	21,647
Held to maturity, gross unrealized gains	76	24
Held to maturity, gross unrealized losses	250	518
Investment securities held-to-maturity	22,394	21,153
Total U.S. Treasury and federal agencies
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	21,055	17,147
Available for sale, gross unrealized gains	138	41
Available for sale, gross unrealized losses	109	181
Investment securities available-for-sale	21,084	17,007
Held to maturity, amortized cost	35,937	36,441
Held to maturity, gross unrealized gains	76	24
Held to maturity, gross unrealized losses	373	717
Investment securities held-to-maturity	35,640	35,748
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	477	538
Available for sale, gross unrealized gains	4	4
Available for sale, gross unrealized losses	0	1
Investment securities available-for-sale	481	541
Held to maturity, amortized cost	3,286	3,191
Held to maturity, gross unrealized gains	26	35
Held to maturity, gross unrealized losses	16	10
Investment securities held-to-maturity	3,296	3,216
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	612	609
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	26	26
Investment securities available-for-sale	586	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	889	594
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	3	2
Investment securities available-for-sale	886	593
Held to maturity, amortized cost	1	1
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	1	1
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,978	1,741
Available for sale, gross unrealized gains	4	5
Available for sale, gross unrealized losses	29	29
Investment securities available-for-sale	1,953	1,717
Held to maturity, amortized cost	3,287	3,385
Held to maturity, gross unrealized gains	26	35
Held to maturity, gross unrealized losses	16	10
Investment securities held-to-maturity	3,297	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	1,520	1,687
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	4	5
Investment securities available-for-sale	1,517	1,682
Held to maturity, amortized cost	575	638
Held to maturity, gross unrealized gains	82	77
Held to maturity, gross unrealized losses	8	9
Investment securities held-to-maturity	649	706
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,517	1,580
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	6	6
Investment securities available-for-sale	1,511	1,574
Held to maturity, amortized cost	98	223
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	98	223
Non-U.S. debt securities, government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,489	12,816
Available for sale, gross unrealized gains	97	22
Available for sale, gross unrealized losses	14	45
Investment securities available-for-sale	12,572	12,793
Held to maturity, amortized cost	399	358
Held to maturity, gross unrealized gains	1	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	400	359
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,520	6,600
Available for sale, gross unrealized gains	59	18
Available for sale, gross unrealized losses	3	16
Investment securities available-for-sale	6,576	6,602
Held to maturity, amortized cost	44	46
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	44	46
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,046	22,683
Available for sale, gross unrealized gains	157	40
Available for sale, gross unrealized losses	27	72
Investment securities available-for-sale	22,176	22,651
Held to maturity, amortized cost	1,116	1,265
Held to maturity, gross unrealized gains	83	78
Held to maturity, gross unrealized losses	8	9
Investment securities held-to-maturity	1,191	1,334
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,903	1,905
Available for sale, gross unrealized gains	39	20
Available for sale, gross unrealized losses	2	7
Investment securities available-for-sale	1,940	1,918
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	130	200
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	1	3
Investment securities available-for-sale	129	197
Held to maturity, amortized cost	805	823
Held to maturity, gross unrealized gains	40	38
Held to maturity, gross unrealized losses	2	2
Investment securities held-to-maturity	843	859
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,715	1,683
Available for sale, gross unrealized gains	12	1
Available for sale, gross unrealized losses	7	26
Investment securities available-for-sale	$ 1,720	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	$ 1,050	1,300
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	1,330	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