Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 13,090
Available for sale, 1 to 5 Years	21,716
Available for sale, 6 to 10 Years	16,535
Available for sale, over 10 Years	20,928
Available-for-sale, fair value	72,269
Held to maturity, under 1 Year	1,023
Held to maturity, 1 to 5 Years	15,153
Held to maturity, 6 to 10 Years	9,636
Held to maturity, over 10 Years	4,574
Held to maturity, amortized cost	30,386	$ 29,952
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,508
Available for sale, 1 to 5 Years	1,154
Available for sale, 6 to 10 Years	252
Available for sale, over 10 Years	418
Available-for-sale, fair value	6,332
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	12,728
Held to maturity, 6 to 10 Years	8,771
Held to maturity, over 10 Years	78
Held to maturity, amortized cost	21,577	20,878
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	103
Available for sale, 1 to 5 Years	2,145
Available for sale, 6 to 10 Years	4,288
Available for sale, over 10 Years	12,539
Available-for-sale, fair value	19,075
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	10
Held to maturity, 6 to 10 Years	171
Held to maturity, over 10 Years	1,340
Held to maturity, amortized cost	1,521	610
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	426
Available for sale, 1 to 5 Years	3,782
Available for sale, 6 to 10 Years	1,354
Available for sale, over 10 Years	1,392
Available-for-sale, fair value	6,954
Held to maturity, under 1 Year	91
Held to maturity, 1 to 5 Years	99
Held to maturity, 6 to 10 Years	229
Held to maturity, over 10 Years	1,070
Held to maturity, amortized cost	1,489	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	261
Available for sale, 6 to 10 Years	1,115
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,380
Held to maturity, under 1 Year	39
Held to maturity, 1 to 5 Years	823
Held to maturity, 6 to 10 Years	35
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	362
Available-for-sale, fair value	369
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2
Available for sale, 1 to 5 Years	158
Available for sale, 6 to 10 Years	1,401
Available for sale, over 10 Years	149
Available-for-sale, fair value	1,710
Held to maturity, under 1 Year	30
Held to maturity, 1 to 5 Years	55
Held to maturity, 6 to 10 Years	51
Held to maturity, over 10 Years	2
Held to maturity, amortized cost	138	366
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	435
Available for sale, 1 to 5 Years	4,203
Available for sale, 6 to 10 Years	3,872
Available for sale, over 10 Years	1,903
Available-for-sale, fair value	10,413
Held to maturity, under 1 Year	160
Held to maturity, 1 to 5 Years	977
Held to maturity, 6 to 10 Years	315
Held to maturity, over 10 Years	1,072
Held to maturity, amortized cost	2,524	2,855
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	876
Available for sale, 1 to 5 Years	4,091
Available for sale, 6 to 10 Years	709
Available for sale, over 10 Years	1,592
Available-for-sale, fair value	7,268
Held to maturity, under 1 Year	323
Held to maturity, 1 to 5 Years	470
Held to maturity, 6 to 10 Years	79
Held to maturity, over 10 Years	1,028
Held to maturity, amortized cost	1,900	2,202
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	125
Available for sale, 1 to 5 Years	2,196
Available for sale, 6 to 10 Years	218
Available for sale, over 10 Years	129
Available-for-sale, fair value	2,668
Held to maturity, under 1 Year	197
Held to maturity, 1 to 5 Years	673
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	870	1,415
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3,907
Available for sale, 1 to 5 Years	1,354
Available for sale, 6 to 10 Years	144
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,405
Held to maturity, under 1 Year	197
Held to maturity, 1 to 5 Years	112
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	309	239
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,794
Available for sale, 1 to 5 Years	3,064
Available for sale, 6 to 10 Years	517
Available for sale, over 10 Years	(1)
Available-for-sale, fair value	5,374
Held to maturity, under 1 Year	74
Held to maturity, 1 to 5 Years	117
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	191	65
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6,702
Available for sale, 1 to 5 Years	10,705
Available for sale, 6 to 10 Years	1,588
Available for sale, over 10 Years	1,720
Available-for-sale, fair value	20,715
Held to maturity, under 1 Year	791
Held to maturity, 1 to 5 Years	1,372
Held to maturity, 6 to 10 Years	79
Held to maturity, over 10 Years	1,028
Held to maturity, amortized cost	3,270	3,921
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	428
Available for sale, 1 to 5 Years	2,314
Available for sale, 6 to 10 Years	5,630
Available for sale, over 10 Years	2,231
Available-for-sale, fair value	10,603
Held to maturity, amortized cost	0	1
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	108
Available for sale, 1 to 5 Years	46
Available for sale, 6 to 10 Years	515
Available for sale, over 10 Years	2,072
Available-for-sale, fair value	2,741
Held to maturity, under 1 Year	72
Held to maturity, 1 to 5 Years	66
Held to maturity, 6 to 10 Years	300
Held to maturity, over 10 Years	1,056
Held to maturity, amortized cost	1,494	$ 1,687
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	806
Available for sale, 1 to 5 Years	1,149
Available for sale, 6 to 10 Years	390
Available for sale, over 10 Years	45
Available-for-sale, fair value	$ 2,390