Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 58,658	$ 62,056
Available for sale, gross unrealized gains	483	427
Available for sale, gross unrealized losses	331	485
Investment securities available-for-sale	58,810	61,998
Held to maturity, amortized cost	35,829	35,169
Held to maturity, gross unrealized gains	180	160
Held to maturity, gross unrealized losses	315	335
Investment securities held-to-maturity	35,694	34,994
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,149	4,265
Available for sale, gross unrealized gains	3	7
Available for sale, gross unrealized losses	1	9
Investment securities available-for-sale	3,151	4,263
Held to maturity, amortized cost	17,504	17,527
Held to maturity, gross unrealized gains	18	17
Held to maturity, gross unrealized losses	44	58
Investment securities held-to-maturity	17,478	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	11,379	13,340
Available for sale, gross unrealized gains	71	76
Available for sale, gross unrealized losses	102	159
Investment securities available-for-sale	11,348	13,257
Held to maturity, amortized cost	11,254	10,334
Held to maturity, gross unrealized gains	26	20
Held to maturity, gross unrealized losses	229	221
Investment securities held-to-maturity	11,051	10,133
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,702	5,659
Available for sale, gross unrealized gains	26	12
Available for sale, gross unrealized losses	37	75
Investment securities available-for-sale	5,691	5,596
Held to maturity, amortized cost	2,812	2,883
Held to maturity, gross unrealized gains	13	5
Held to maturity, gross unrealized losses	20	30
Investment securities held-to-maturity	2,805	2,858
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,323	1,377
Available for sale, gross unrealized gains	1	0
Available for sale, gross unrealized losses	22	26
Investment securities available-for-sale	1,302	1,351
Held to maturity, amortized cost	858	897
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	861	899
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	264	289
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	14	18
Investment securities available-for-sale	252	272
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	863	895
Available for sale, gross unrealized gains	8	10
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	871	905
Held to maturity, amortized cost	15	35
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	15	35
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,152	8,220
Available for sale, gross unrealized gains	37	23
Available for sale, gross unrealized losses	73	119
Investment securities available-for-sale	8,116	8,124
Held to maturity, amortized cost	3,685	3,815
Held to maturity, gross unrealized gains	16	7
Held to maturity, gross unrealized losses	20	30
Investment securities held-to-maturity	3,681	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	6,550	6,506
Available for sale, gross unrealized gains	38	35
Available for sale, gross unrealized losses	5	6
Investment securities available-for-sale	6,583	6,535
Held to maturity, amortized cost	1,131	1,150
Held to maturity, gross unrealized gains	76	70
Held to maturity, gross unrealized losses	12	15
Investment securities held-to-maturity	1,195	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	2,806	2,513
Available for sale, gross unrealized gains	6	4
Available for sale, gross unrealized losses	1	1
Investment securities available-for-sale	2,811	2,516
Held to maturity, amortized cost	437	531
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	438	531
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,810	5,834
Available for sale, gross unrealized gains	7	8
Available for sale, gross unrealized losses	13	6
Investment securities available-for-sale	5,804	5,836
Held to maturity, amortized cost	340	286
Held to maturity, gross unrealized gains	2	3
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	342	289
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,776	5,587
Available for sale, gross unrealized gains	31	31
Available for sale, gross unrealized losses	5	5
Investment securities available-for-sale	5,802	5,613
Held to maturity, amortized cost	117	113
Held to maturity, gross unrealized gains	2	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	119	114
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,942	20,440
Available for sale, gross unrealized gains	82	78
Available for sale, gross unrealized losses	24	18
Investment securities available-for-sale	21,000	20,500
Held to maturity, amortized cost	2,025	2,080
Held to maturity, gross unrealized gains	81	74
Held to maturity, gross unrealized losses	12	15
Investment securities held-to-maturity	2,094	2,139
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,640	10,233
Available for sale, gross unrealized gains	252	201
Available for sale, gross unrealized losses	70	112
Investment securities available-for-sale	9,822	10,322
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,480	2,610
Available for sale, gross unrealized gains	15	18
Available for sale, gross unrealized losses	34	35
Investment securities available-for-sale	2,461	2,593
Held to maturity, amortized cost	1,361	1,413
Held to maturity, gross unrealized gains	39	42
Held to maturity, gross unrealized losses	10	11
Investment securities held-to-maturity	1,390	1,444
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,435	2,481
Available for sale, gross unrealized gains	16	18
Available for sale, gross unrealized losses	25	30
Investment securities available-for-sale	2,426	2,469
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	39	39
Available for sale, gross unrealized gains	7	6
Available for sale, gross unrealized losses	2	3
Investment securities available-for-sale	44	42
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2	3
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	2	3
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	424	409
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	424	409
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	16	16
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	$ 16	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	$ 871	905
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	3,742	3,769
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 1,054	$ 988