Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 70,795	$ 69,843
Available for sale, gross unrealized gains	1,016	735
Available for sale, gross unrealized losses	291	508
Investment securities available for sale	71,520	70,070
Held to maturity, amortized cost	28,368	29,952
Held to maturity, gross unrealized gains	487	179
Held to maturity, gross unrealized losses	75	333
Held to maturity, fair value	28,780	29,798
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,283	5,717
Available for sale, gross unrealized gains	20	6
Available for sale, gross unrealized losses	1	5
Investment securities available for sale	5,302	5,718
Held to maturity, amortized cost	17,553	20,878
Held to maturity, gross unrealized gains	333	2
Held to maturity, gross unrealized losses	1	217
Held to maturity, fair value	17,885	20,663
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	17,796	18,168
Available for sale, gross unrealized gains	224	131
Available for sale, gross unrealized losses	25	134
Investment securities available for sale	17,995	18,165
Held to maturity, amortized cost	4,280	610
Held to maturity, gross unrealized gains	20	2
Held to maturity, gross unrealized losses	3	8
Held to maturity, fair value	4,297	604
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,451	7,358
Available for sale, gross unrealized gains	19	16
Available for sale, gross unrealized losses	163	198
Investment securities available for sale	7,307	7,176
Held to maturity, amortized cost	1,440	1,592
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	40	47
Held to maturity, fair value	1,400	1,545
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,388	1,378
Available for sale, gross unrealized gains	12	0
Available for sale, gross unrealized losses	25	37
Investment securities available for sale	1,375	1,341
Held to maturity, amortized cost	897	897
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	900	896
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	376	448
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	24	31
Investment securities available for sale	354	419
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,257	1,724
Available for sale, gross unrealized gains	16	43
Available for sale, gross unrealized losses	0	3
Investment securities available for sale	1,273	1,764
Held to maturity, amortized cost	76	366
Held to maturity, gross unrealized gains	0	2
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	76	367
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,472	10,908
Available for sale, gross unrealized gains	49	61
Available for sale, gross unrealized losses	212	269
Investment securities available for sale	10,309	10,700
Held to maturity, amortized cost	2,413	2,855
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	40	49
Held to maturity, fair value	2,376	2,808
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,122	7,010
Available for sale, gross unrealized gains	48	72
Available for sale, gross unrealized losses	9	11
Investment securities available for sale	7,161	7,071
Held to maturity, amortized cost	1,581	2,202
Held to maturity, gross unrealized gains	84	109
Held to maturity, gross unrealized losses	17	26
Held to maturity, fair value	1,648	2,285
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,528	3,272
Available for sale, gross unrealized gains	4	2
Available for sale, gross unrealized losses	3	7
Investment securities available for sale	2,529	3,267
Held to maturity, amortized cost	697	1,415
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	1	3
Held to maturity, fair value	696	1,416
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,967	4,348
Available for sale, gross unrealized gains	17	7
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	5,984	4,355
Held to maturity, amortized cost	288	239
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	291	238
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,876	4,817
Available for sale, gross unrealized gains	44	29
Available for sale, gross unrealized losses	1	12
Investment securities available for sale	5,919	4,834
Held to maturity, amortized cost	119	65
Held to maturity, gross unrealized gains	2	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	121	65
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	21,493	19,447
Available for sale, gross unrealized gains	113	110
Available for sale, gross unrealized losses	13	30
Investment securities available for sale	21,593	19,527
Held to maturity, amortized cost	2,685	3,921
Held to maturity, gross unrealized gains	89	113
Held to maturity, gross unrealized losses	18	30
Held to maturity, fair value	2,756	4,004
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,274	9,402
Available for sale, gross unrealized gains	505	371
Available for sale, gross unrealized losses	23	27
Investment securities available for sale	10,756	9,746
Held to maturity, amortized cost	0	1
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	0	1
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,752	2,993
Available for sale, gross unrealized gains	62	16
Available for sale, gross unrealized losses	8	22
Investment securities available for sale	2,806	2,987
Held to maturity, amortized cost	1,437	1,687
Held to maturity, gross unrealized gains	42	60
Held to maturity, gross unrealized losses	13	29
Held to maturity, fair value	1,466	1,718
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,306	2,611
Available for sale, gross unrealized gains	39	31
Available for sale, gross unrealized losses	7	18
Investment securities available for sale	2,338	2,624
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	39	33
Available for sale, gross unrealized gains	4	9
Available for sale, gross unrealized losses	2	3
Investment securities available for sale	41	39
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3	3
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	3	3
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	361	542
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	361	542
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	16	19
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	$ 16	19
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	$ 1,270	1,760
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,980	3,180
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 981	$ 613