Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 58,714	$ 62,056
Available for sale, gross unrealized gains	571	427
Available for sale, gross unrealized losses	260	485
Investment securities available-for-sale	59,025	61,998
Held to maturity, amortized cost	36,230	35,169
Held to maturity, gross unrealized gains	206	160
Held to maturity, gross unrealized losses	267	335
Investment securities held-to-maturity	36,169	34,994
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	632	4,265
Available for sale, gross unrealized gains	3	7
Available for sale, gross unrealized losses	2	9
Investment securities available-for-sale	633	4,263
Held to maturity, amortized cost	17,479	17,527
Held to maturity, gross unrealized gains	27	17
Held to maturity, gross unrealized losses	35	58
Investment securities held-to-maturity	17,471	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	11,445	13,340
Available for sale, gross unrealized gains	61	76
Available for sale, gross unrealized losses	92	159
Investment securities available-for-sale	11,414	13,257
Held to maturity, amortized cost	11,937	10,334
Held to maturity, gross unrealized gains	35	20
Held to maturity, gross unrealized losses	200	221
Investment securities held-to-maturity	11,772	10,133
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,871	5,659
Available for sale, gross unrealized gains	36	12
Available for sale, gross unrealized losses	20	75
Investment securities available-for-sale	5,887	5,596
Held to maturity, amortized cost	2,738	2,883
Held to maturity, gross unrealized gains	17	5
Held to maturity, gross unrealized losses	15	30
Investment securities held-to-maturity	2,740	2,858
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,575	1,377
Available for sale, gross unrealized gains	3	0
Available for sale, gross unrealized losses	22	26
Investment securities available-for-sale	1,556	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	249	289
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	8	18
Investment securities available-for-sale	243	272
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,154	895
Available for sale, gross unrealized gains	6	10
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	1,160	905
Held to maturity, amortized cost	5	35
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	5	35
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,849	8,220
Available for sale, gross unrealized gains	47	23
Available for sale, gross unrealized losses	50	119
Investment securities available-for-sale	8,846	8,124
Held to maturity, amortized cost	3,601	3,815
Held to maturity, gross unrealized gains	20	7
Held to maturity, gross unrealized losses	15	30
Investment securities held-to-maturity	3,606	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	6,925	6,506
Available for sale, gross unrealized gains	40	35
Available for sale, gross unrealized losses	3	6
Investment securities available-for-sale	6,962	6,535
Held to maturity, amortized cost	1,084	1,150
Held to maturity, gross unrealized gains	80	70
Held to maturity, gross unrealized losses	10	15
Investment securities held-to-maturity	1,154	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	2,884	2,513
Available for sale, gross unrealized gains	7	4
Available for sale, gross unrealized losses	0	1
Investment securities available-for-sale	2,891	2,516
Held to maturity, amortized cost	365	531
Held to maturity, gross unrealized gains	1	0
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	366	531
Non-U.S. debt securities, Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,614	5,834
Available for sale, gross unrealized gains	6	8
Available for sale, gross unrealized losses	20	6
Investment securities available-for-sale	6,600	5,836
Held to maturity, amortized cost	357	286
Held to maturity, gross unrealized gains	2	3
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	359	289
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	6,247	5,587
Available for sale, gross unrealized gains	34	31
Available for sale, gross unrealized losses	5	5
Investment securities available-for-sale	6,276	5,613
Held to maturity, amortized cost	122	113
Held to maturity, gross unrealized gains	0	1
Held to maturity, gross unrealized losses	0	0
Investment securities held-to-maturity	122	114
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	22,670	20,440
Available for sale, gross unrealized gains	87	78
Available for sale, gross unrealized losses	28	18
Investment securities available-for-sale	22,729	20,500
Held to maturity, amortized cost	1,928	2,080
Held to maturity, gross unrealized gains	83	74
Held to maturity, gross unrealized losses	10	15
Investment securities held-to-maturity	2,001	2,139
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,747	10,233
Available for sale, gross unrealized gains	328	201
Available for sale, gross unrealized losses	37	112
Investment securities available-for-sale	10,038	10,322
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,449	2,610
Available for sale, gross unrealized gains	21	18
Available for sale, gross unrealized losses	27	35
Investment securities available-for-sale	2,443	2,593
Held to maturity, amortized cost	1,285	1,413
Held to maturity, gross unrealized gains	41	42
Held to maturity, gross unrealized losses	7	11
Investment securities held-to-maturity	1,319	1,444
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,804	2,481
Available for sale, gross unrealized gains	17	18
Available for sale, gross unrealized losses	22	30
Investment securities available-for-sale	2,799	2,469
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	40	39
Available for sale, gross unrealized gains	7	6
Available for sale, gross unrealized losses	2	3
Investment securities available-for-sale	45	42
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1	3
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	1	3
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	77	409
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	77	409
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	0	16
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available-for-sale	$ 0	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	$ 1,160	905
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	3,968	3,769
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available-for-sale	$ 1,264	$ 988