Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 55,882	$ 62,056
Available for sale, gross unrealized gains	559	427
Available for sale, gross unrealized losses	203	485
Investment securities available-for-sale	56,238	61,998
Held to maturity, amortized cost	36,850	35,169
Held to maturity, gross unrealized gains	217	160
Held to maturity, gross unrealized losses	231	335
Investment securities held-to-maturity	36,836	34,994
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	617	4,265
Available for sale, gross unrealized gains	4	7
Available for sale, gross unrealized losses	1	9
Investment securities available-for-sale	620	4,263
Held to maturity, amortized cost	17,456	17,527
Held to maturity, gross unrealized gains	20	17
Held to maturity, gross unrealized losses	37	58
Investment securities held-to-maturity	17,439	17,486
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	11,044	13,340
Available for sale, gross unrealized gains	51	76
Available for sale, gross unrealized losses	95	159
Investment securities available-for-sale	11,000	13,257
Held to maturity, amortized cost	12,375	10,334
Held to maturity, gross unrealized gains	38	20
Held to maturity, gross unrealized losses	169	221
Investment securities held-to-maturity	12,244	10,133
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,795	5,659
Available for sale, gross unrealized gains	39	12
Available for sale, gross unrealized losses	8	75
Investment securities available-for-sale	4,826	5,596
Held to maturity, amortized cost	3,116	2,883
Held to maturity, gross unrealized gains	25	5
Held to maturity, gross unrealized losses	13	30
Investment securities held-to-maturity	3,128	2,858
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,567	1,377
Available for sale, gross unrealized gains	3	0
Available for sale, gross unrealized losses	22	26
Investment securities available-for-sale	1,548	1,351
Held to maturity, amortized cost	798	897
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	801	899
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	0	289
Available for sale, gross unrealized gains	0	1
Available for sale, gross unrealized losses	0	18
Investment securities available-for-sale	0	272
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,213	895
Available for sale, gross unrealized gains	8	10
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	1,221	905
Held to maturity, amortized cost	1	35
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	1	35
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,575	8,220
Available for sale, gross unrealized gains	50	23
Available for sale, gross unrealized losses	30	119
Investment securities available-for-sale	7,595	8,124
Held to maturity, amortized cost	3,915	3,815
Held to maturity, gross unrealized gains	28	7
Held to maturity, gross unrealized losses	13	30
Investment securities held-to-maturity	3,930	3,792
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,041	6,506
Available for sale, gross unrealized gains	36	35
Available for sale, gross unrealized losses	3	6
Investment securities available-for-sale	7,074	6,535
Held to maturity, amortized cost	1,000	1,150
Held to maturity, gross unrealized gains	84	70
Held to maturity, gross unrealized losses	7	15
Investment securities held-to-maturity	1,077	1,205
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,833	2,513
Available for sale, gross unrealized gains	6	4
Available for sale, gross unrealized losses	0	1
Investment securities available-for-sale	2,839	2,516
Held to maturity, amortized cost	325	531
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	326	531
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,666	5,834
Available for sale, gross unrealized gains	8	8
Available for sale, gross unrealized losses	16	6
Investment securities available-for-sale	6,658	5,836
Held to maturity, amortized cost	483	286
Held to maturity, gross unrealized gains	2	3
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	485	289
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,783	5,587
Available for sale, gross unrealized gains	39	31
Available for sale, gross unrealized losses	4	5
Investment securities available-for-sale	5,818	5,613
Held to maturity, amortized cost	47	113
Held to maturity, gross unrealized gains	0	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	47	114
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,323	20,440
Available for sale, gross unrealized gains	89	78
Available for sale, gross unrealized losses	23	18
Investment securities available-for-sale	22,389	20,500
Held to maturity, amortized cost	1,855	2,080
Held to maturity, gross unrealized gains	87	74
Held to maturity, gross unrealized losses	7	15
Investment securities held-to-maturity	1,935	2,139
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,444	10,233
Available for sale, gross unrealized gains	322	201
Available for sale, gross unrealized losses	28	112
Investment securities available-for-sale	9,738	10,322
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,522	2,610
Available for sale, gross unrealized gains	15	18
Available for sale, gross unrealized losses	9	35
Investment securities available-for-sale	1,528	2,593
Held to maturity, amortized cost	1,249	1,413
Held to maturity, gross unrealized gains	44	42
Held to maturity, gross unrealized losses	5	11
Investment securities held-to-maturity	1,288	1,444
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,923	2,481
Available for sale, gross unrealized gains	20	18
Available for sale, gross unrealized losses	15	30
Investment securities available-for-sale	2,928	2,469
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	40	39
Available for sale, gross unrealized gains	8	6
Available for sale, gross unrealized losses	2	3
Investment securities available-for-sale	46	42
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	0	3
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	0	3
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	394	409
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	394	409
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	0	16
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	$ 0	16
Federal family education loan program
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Federal government credit support guarantee, percentage minimum	97.00%
Collateralized loan obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 1,221	905
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	3,600	3,769
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 1,503	$ 988