Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 71,940	$ 69,843
Available for sale, gross unrealized gains	1,163	735
Available for sale, gross unrealized losses	368	508
Investment securities available for sale	72,735	70,070
Held to maturity, amortized cost	30,386	29,952
Held to maturity, gross unrealized gains	615	179
Held to maturity, gross unrealized losses	106	333
Held to maturity, fair value	30,895	29,798
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,301	5,717
Available for sale, gross unrealized gains	32	6
Available for sale, gross unrealized losses	1	5
Investment securities available for sale	6,332	5,718
Held to maturity, amortized cost	21,577	20,878
Held to maturity, gross unrealized gains	446	2
Held to maturity, gross unrealized losses	1	217
Held to maturity, fair value	22,022	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	18,788	18,168
Available for sale, gross unrealized gains	298	131
Available for sale, gross unrealized losses	11	134
Investment securities available for sale	19,075	18,165
Held to maturity, amortized cost	1,521	610
Held to maturity, gross unrealized gains	14	2
Held to maturity, gross unrealized losses	0	8
Held to maturity, fair value	1,535	604
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,162	7,358
Available for sale, gross unrealized gains	8	16
Available for sale, gross unrealized losses	216	198
Investment securities available for sale	6,954	7,176
Held to maturity, amortized cost	1,489	1,592
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	51	47
Held to maturity, fair value	1,438	1,545
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,392	1,378
Available for sale, gross unrealized gains	15	0
Available for sale, gross unrealized losses	27	37
Investment securities available for sale	1,380	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	396	448
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	28	31
Investment securities available for sale	369	419
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,684	1,724
Available for sale, gross unrealized gains	27	43
Available for sale, gross unrealized losses	1	3
Investment securities available for sale	1,710	1,764
Held to maturity, amortized cost	138	366
Held to maturity, gross unrealized gains	1	2
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	139	367
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,634	10,908
Available for sale, gross unrealized gains	51	61
Available for sale, gross unrealized losses	272	269
Investment securities available for sale	10,413	10,700
Held to maturity, amortized cost	2,524	2,855
Held to maturity, gross unrealized gains	2	2
Held to maturity, gross unrealized losses	51	49
Held to maturity, fair value	2,475	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	7,254	7,010
Available for sale, gross unrealized gains	42	72
Available for sale, gross unrealized losses	28	11
Investment securities available for sale	7,268	7,071
Held to maturity, amortized cost	1,900	2,202
Held to maturity, gross unrealized gains	96	109
Held to maturity, gross unrealized losses	31	26
Held to maturity, fair value	1,965	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	2,675	3,272
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	9	7
Investment securities available for sale	2,668	3,267
Held to maturity, amortized cost	870	1,415
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	4	3
Held to maturity, fair value	866	1,416
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,385	4,348
Available for sale, gross unrealized gains	20	7
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	5,405	4,355
Held to maturity, amortized cost	309	239
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	312	238
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,341	4,817
Available for sale, gross unrealized gains	37	29
Available for sale, gross unrealized losses	4	12
Investment securities available for sale	5,374	4,834
Held to maturity, amortized cost	191	65
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	194	65
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,655	19,447
Available for sale, gross unrealized gains	101	110
Available for sale, gross unrealized losses	41	30
Investment securities available for sale	20,715	19,527
Held to maturity, amortized cost	3,270	3,921
Held to maturity, gross unrealized gains	102	113
Held to maturity, gross unrealized losses	35	30
Held to maturity, fair value	3,337	4,004
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,065	9,402
Available for sale, gross unrealized gains	563	371
Available for sale, gross unrealized losses	25	27
Investment securities available for sale	10,603	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	2,681	2,993
Available for sale, gross unrealized gains	66	16
Available for sale, gross unrealized losses	6	22
Investment securities available for sale	2,741	2,987
Held to maturity, amortized cost	1,494	1,687
Held to maturity, gross unrealized gains	51	60
Held to maturity, gross unrealized losses	19	29
Held to maturity, fair value	1,526	1,718
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,357	2,611
Available for sale, gross unrealized gains	42	31
Available for sale, gross unrealized losses	9	18
Investment securities available for sale	2,390	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	10	9
Available for sale, gross unrealized losses	3	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	405	542
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	405	542
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	17	19
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	$ 17	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	$ 1,710	1,760
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,400	3,180
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 970	$ 613