Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 13,136
Available for sale, 1 to 5 Years	22,213
Available for sale, 6 to 10 Years	15,832
Available for sale, over 10 Years	19,918
Available-for-sale, fair value	71,099
Held to maturity, under 1 Year	1,066
Held to maturity, 1 to 5 Years	16,856
Held to maturity, 6 to 10 Years	3,555
Held to maturity, over 10 Years	6,891
Held to maturity, amortized cost	28,368	$ 29,952
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3,504
Available for sale, 1 to 5 Years	1,250
Available for sale, 6 to 10 Years	146
Available for sale, over 10 Years	402
Available-for-sale, fair value	5,302
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	14,732
Held to maturity, 6 to 10 Years	2,745
Held to maturity, over 10 Years	76
Held to maturity, amortized cost	17,553	20,878
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	61
Available for sale, 1 to 5 Years	1,940
Available for sale, 6 to 10 Years	4,343
Available for sale, over 10 Years	11,651
Available-for-sale, fair value	17,995
Held to maturity, under 1 Year	1
Held to maturity, 1 to 5 Years	8
Held to maturity, 6 to 10 Years	167
Held to maturity, over 10 Years	4,104
Held to maturity, amortized cost	4,280	610
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	894
Available for sale, 1 to 5 Years	3,376
Available for sale, 6 to 10 Years	1,132
Available for sale, over 10 Years	1,905
Available-for-sale, fair value	7,307
Held to maturity, under 1 Year	89
Held to maturity, 1 to 5 Years	175
Held to maturity, 6 to 10 Years	230
Held to maturity, over 10 Years	946
Held to maturity, amortized cost	1,440	1,592
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4
Available for sale, 1 to 5 Years	1,068
Available for sale, 6 to 10 Years	303
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,375
Held to maturity, under 1 Year	98
Held to maturity, 1 to 5 Years	799
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	897	897
Asset-backed securities, sub-prime
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3
Available for sale, 1 to 5 Years	2
Available for sale, 6 to 10 Years	2
Available for sale, over 10 Years	347
Available-for-sale, fair value	354
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3
Available for sale, 1 to 5 Years	84
Available for sale, 6 to 10 Years	1,036
Available for sale, over 10 Years	150
Available-for-sale, fair value	1,273
Held to maturity, under 1 Year	13
Held to maturity, 1 to 5 Years	26
Held to maturity, 6 to 10 Years	34
Held to maturity, over 10 Years	3
Held to maturity, amortized cost	76	366
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	904
Available for sale, 1 to 5 Years	4,530
Available for sale, 6 to 10 Years	2,473
Available for sale, over 10 Years	2,402
Available-for-sale, fair value	10,309
Held to maturity, under 1 Year	200
Held to maturity, 1 to 5 Years	1,000
Held to maturity, 6 to 10 Years	264
Held to maturity, over 10 Years	949
Held to maturity, amortized cost	2,413	2,855
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,239
Available for sale, 1 to 5 Years	3,734
Available for sale, 6 to 10 Years	850
Available for sale, over 10 Years	1,338
Available-for-sale, fair value	7,161
Held to maturity, under 1 Year	368
Held to maturity, 1 to 5 Years	387
Held to maturity, 6 to 10 Years	74
Held to maturity, over 10 Years	752
Held to maturity, amortized cost	1,581	2,202
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	80
Available for sale, 1 to 5 Years	2,214
Available for sale, 6 to 10 Years	229
Available for sale, over 10 Years	6
Available-for-sale, fair value	2,529
Held to maturity, under 1 Year	145
Held to maturity, 1 to 5 Years	546
Held to maturity, 6 to 10 Years	6
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	697	1,415
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,453
Available for sale, 1 to 5 Years	1,319
Available for sale, 6 to 10 Years	212
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,984
Held to maturity, under 1 Year	175
Held to maturity, 1 to 5 Years	113
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	288	239
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,818
Available for sale, 1 to 5 Years	3,710
Available for sale, 6 to 10 Years	391
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,919
Held to maturity, under 1 Year	74
Held to maturity, 1 to 5 Years	45
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	119	65
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	7,590
Available for sale, 1 to 5 Years	10,977
Available for sale, 6 to 10 Years	1,682
Available for sale, over 10 Years	1,344
Available-for-sale, fair value	21,593
Held to maturity, under 1 Year	762
Held to maturity, 1 to 5 Years	1,091
Held to maturity, 6 to 10 Years	80
Held to maturity, over 10 Years	752
Held to maturity, amortized cost	2,685	3,921
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	460
Available for sale, 1 to 5 Years	2,387
Available for sale, 6 to 10 Years	5,730
Available for sale, over 10 Years	2,179
Available-for-sale, fair value	10,756
Held to maturity, amortized cost	0	1
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	16
Available for sale, 1 to 5 Years	55
Available for sale, 6 to 10 Years	842
Available for sale, over 10 Years	1,893
Available-for-sale, fair value	2,806
Held to maturity, under 1 Year	103
Held to maturity, 1 to 5 Years	25
Held to maturity, 6 to 10 Years	299
Held to maturity, over 10 Years	1,010
Held to maturity, amortized cost	1,437	$ 1,687
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	601
Available for sale, 1 to 5 Years	1,074
Available for sale, 6 to 10 Years	616
Available for sale, over 10 Years	47
Available-for-sale, fair value	$ 2,338