Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 62,056	$ 69,843
Available for sale, gross unrealized gains	427	735
Available for sale, gross unrealized losses	485	508
Investment securities available-for-sale	61,998	70,070
Held to maturity, amortized cost	35,169	29,952
Held to maturity, gross unrealized gains	160	179
Held to maturity, gross unrealized losses	335	333
Held to maturity, fair value	34,994	29,798
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,265	5,717
Available for sale, gross unrealized gains	7	6
Available for sale, gross unrealized losses	9	5
Investment securities available-for-sale	4,263	5,718
Held to maturity, amortized cost	17,527	20,878
Held to maturity, gross unrealized gains	17	2
Held to maturity, gross unrealized losses	58	217
Held to maturity, fair value	17,486	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	13,340	18,168
Available for sale, gross unrealized gains	76	131
Available for sale, gross unrealized losses	159	134
Investment securities available-for-sale	13,257	18,165
Held to maturity, amortized cost	10,334	610
Held to maturity, gross unrealized gains	20	2
Held to maturity, gross unrealized losses	221	8
Held to maturity, fair value	10,133	604
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,659	7,358
Available for sale, gross unrealized gains	12	16
Available for sale, gross unrealized losses	75	198
Investment securities available-for-sale	5,596	7,176
Held to maturity, amortized cost	2,883	1,592
Held to maturity, gross unrealized gains	5	0
Held to maturity, gross unrealized losses	30	47
Held to maturity, fair value	2,858	1,545
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,377	1,378
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	26	37
Investment securities available-for-sale	1,351	1,341
Held to maturity, amortized cost	897	897
Held to maturity, gross unrealized gains	2	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	899	896
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	289	448
Available for sale, gross unrealized gains	1	2
Available for sale, gross unrealized losses	18	31
Investment securities available-for-sale	272	419
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	895	1,724
Available for sale, gross unrealized gains	10	43
Available for sale, gross unrealized losses	0	3
Investment securities available-for-sale	905	1,764
Held to maturity, amortized cost	35	366
Held to maturity, gross unrealized gains	0	2
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	35	367
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,220	10,908
Available for sale, gross unrealized gains	23	61
Available for sale, gross unrealized losses	119	269
Investment securities available-for-sale	8,124	10,700
Held to maturity, amortized cost	3,815	2,855
Held to maturity, gross unrealized gains	7	2
Held to maturity, gross unrealized losses	30	49
Held to maturity, fair value	3,792	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	6,506	7,010
Available for sale, gross unrealized gains	35	72
Available for sale, gross unrealized losses	6	11
Investment securities available-for-sale	6,535	7,071
Held to maturity, amortized cost	1,150	2,202
Held to maturity, gross unrealized gains	70	109
Held to maturity, gross unrealized losses	15	26
Held to maturity, fair value	1,205	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	2,513	3,272
Available for sale, gross unrealized gains	4	2
Available for sale, gross unrealized losses	1	7
Investment securities available-for-sale	2,516	3,267
Held to maturity, amortized cost	531	1,415
Held to maturity, gross unrealized gains	0	4
Held to maturity, gross unrealized losses	0	3
Held to maturity, fair value	531	1,416
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,834	4,348
Available for sale, gross unrealized gains	8	7
Available for sale, gross unrealized losses	6	0
Investment securities available-for-sale	5,836	4,355
Held to maturity, amortized cost	286	239
Held to maturity, gross unrealized gains	3	0
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	289	238
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,587	4,817
Available for sale, gross unrealized gains	31	29
Available for sale, gross unrealized losses	5	12
Investment securities available-for-sale	5,613	4,834
Held to maturity, amortized cost	113	65
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	114	65
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,440	19,447
Available for sale, gross unrealized gains	78	110
Available for sale, gross unrealized losses	18	30
Investment securities available-for-sale	20,500	19,527
Held to maturity, amortized cost	2,080	3,921
Held to maturity, gross unrealized gains	74	113
Held to maturity, gross unrealized losses	15	30
Held to maturity, fair value	2,139	4,004
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,233	9,402
Available for sale, gross unrealized gains	201	371
Available for sale, gross unrealized losses	112	27
Investment securities available-for-sale	10,322	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	2,610	2,993
Available for sale, gross unrealized gains	18	16
Available for sale, gross unrealized losses	35	22
Investment securities available-for-sale	2,593	2,987
Held to maturity, amortized cost	1,413	1,687
Held to maturity, gross unrealized gains	42	60
Held to maturity, gross unrealized losses	11	29
Held to maturity, fair value	1,444	1,718
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,481	2,611
Available for sale, gross unrealized gains	18	31
Available for sale, gross unrealized losses	30	18
Investment securities available-for-sale	2,469	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	6	9
Available for sale, gross unrealized losses	3	3
Investment securities available-for-sale	42	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	409	542
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	409	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	$ 905	1,764
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	3,769	3,184
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 988	$ 613