Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 70,581	$ 69,843
Available for sale, gross unrealized gains	961	735
Available for sale, gross unrealized losses	456	508
Investment securities available for sale	71,086	70,070
Held to maturity, amortized cost	31,212	29,952
Held to maturity, gross unrealized gains	463	179
Held to maturity, gross unrealized losses	120	333
Held to maturity, fair value	31,555	29,798
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,321	5,717
Available for sale, gross unrealized gains	23	6
Available for sale, gross unrealized losses	2	5
Investment securities available for sale	6,342	5,718
Held to maturity, amortized cost	22,603	20,878
Held to maturity, gross unrealized gains	298	2
Held to maturity, gross unrealized losses	6	217
Held to maturity, fair value	22,895	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	18,028	18,168
Available for sale, gross unrealized gains	243	131
Available for sale, gross unrealized losses	37	134
Investment securities available for sale	18,234	18,165
Held to maturity, amortized cost	588	610
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	0	8
Held to maturity, fair value	591	604
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,052	7,358
Available for sale, gross unrealized gains	9	16
Available for sale, gross unrealized losses	244	198
Investment securities available for sale	6,817	7,176
Held to maturity, amortized cost	1,544	1,592
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	56	47
Held to maturity, fair value	1,488	1,545
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,390	1,378
Available for sale, gross unrealized gains	9	0
Available for sale, gross unrealized losses	31	37
Investment securities available for sale	1,368	1,341
Held to maturity, amortized cost	897	897
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	898	896
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	421	448
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	34	31
Investment securities available for sale	388	419
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,784	1,724
Available for sale, gross unrealized gains	35	43
Available for sale, gross unrealized losses	6	3
Investment securities available for sale	1,813	1,764
Held to maturity, amortized cost	277	366
Held to maturity, gross unrealized gains	0	2
Held to maturity, gross unrealized losses	1	1
Held to maturity, fair value	276	367
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,647	10,908
Available for sale, gross unrealized gains	54	61
Available for sale, gross unrealized losses	315	269
Investment securities available for sale	10,386	10,700
Held to maturity, amortized cost	2,718	2,855
Held to maturity, gross unrealized gains	1	2
Held to maturity, gross unrealized losses	57	49
Held to maturity, fair value	2,662	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	7,581	7,010
Available for sale, gross unrealized gains	57	72
Available for sale, gross unrealized losses	26	11
Investment securities available for sale	7,612	7,071
Held to maturity, amortized cost	2,147	2,202
Held to maturity, gross unrealized gains	104	109
Held to maturity, gross unrealized losses	31	26
Held to maturity, fair value	2,220	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	2,709	3,272
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	7	7
Investment securities available for sale	2,704	3,267
Held to maturity, amortized cost	1,109	1,415
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	4	3
Held to maturity, fair value	1,105	1,416
Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,057	4,348
Available for sale, gross unrealized gains	13	7
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	5,070	4,355
Held to maturity, amortized cost	273	239
Held to maturity, gross unrealized gains	2	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	275	238
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,985	4,817
Available for sale, gross unrealized gains	34	29
Available for sale, gross unrealized losses	10	12
Investment securities available for sale	5,009	4,834
Held to maturity, amortized cost	217	65
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	220	65
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,332	19,447
Available for sale, gross unrealized gains	106	110
Available for sale, gross unrealized losses	43	30
Investment securities available for sale	20,395	19,527
Held to maturity, amortized cost	3,746	3,921
Held to maturity, gross unrealized gains	109	113
Held to maturity, gross unrealized losses	35	30
Held to maturity, fair value	3,820	4,004
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,614	9,402
Available for sale, gross unrealized gains	443	371
Available for sale, gross unrealized losses	31	27
Investment securities available for sale	10,026	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	2,900	2,993
Available for sale, gross unrealized gains	47	16
Available for sale, gross unrealized losses	9	22
Investment securities available for sale	2,938	2,987
Held to maturity, amortized cost	1,557	1,687
Held to maturity, gross unrealized gains	52	60
Held to maturity, gross unrealized losses	22	29
Held to maturity, fair value	1,587	1,718
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,211	2,611
Available for sale, gross unrealized gains	36	31
Available for sale, gross unrealized losses	16	18
Investment securities available for sale	2,231	2,624
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	34	33
Available for sale, gross unrealized gains	9	9
Available for sale, gross unrealized losses	3	3
Investment securities available for sale	40	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	473	542
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	473	542
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	18	19
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	$ 18	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	$ 1,810	1,760
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,380	3,180
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 741	$ 613