Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 10,428
Available for sale, 1 to 5 Years	24,117
Available for sale, 6 to 10 Years	16,442
Available for sale, over 10 Years	19,565
Available-for-sale, fair value	70,552
Held to maturity, under 1 Year	1,105
Held to maturity, 1 to 5 Years	14,632
Held to maturity, 6 to 10 Years	11,555
Held to maturity, over 10 Years	3,920
Held to maturity, amortized cost	31,212	$ 29,952
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,002
Available for sale, 1 to 5 Years	3,654
Available for sale, 6 to 10 Years	246
Available for sale, over 10 Years	440
Available-for-sale, fair value	6,342
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	11,887
Held to maturity, 6 to 10 Years	10,633
Held to maturity, over 10 Years	83
Held to maturity, amortized cost	22,603	20,878
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	117
Available for sale, 1 to 5 Years	2,240
Available for sale, 6 to 10 Years	4,323
Available for sale, over 10 Years	11,554
Available-for-sale, fair value	18,234
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	11
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	577
Held to maturity, amortized cost	588	610
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	465
Available for sale, 1 to 5 Years	3,851
Available for sale, 6 to 10 Years	1,455
Available for sale, over 10 Years	1,046
Available-for-sale, fair value	6,817
Held to maturity, under 1 Year	50
Held to maturity, 1 to 5 Years	142
Held to maturity, 6 to 10 Years	244
Held to maturity, over 10 Years	1,108
Held to maturity, amortized cost	1,544	1,592
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6
Available for sale, 1 to 5 Years	259
Available for sale, 6 to 10 Years	1,103
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,368
Held to maturity, under 1 Year	39
Held to maturity, 1 to 5 Years	641
Held to maturity, 6 to 10 Years	217
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	1
Available for sale, 1 to 5 Years	4
Available for sale, 6 to 10 Years	2
Available for sale, over 10 Years	381
Available-for-sale, fair value	388
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6
Available for sale, 1 to 5 Years	219
Available for sale, 6 to 10 Years	1,439
Available for sale, over 10 Years	149
Available-for-sale, fair value	1,813
Held to maturity, under 1 Year	72
Held to maturity, 1 to 5 Years	134
Held to maturity, 6 to 10 Years	68
Held to maturity, over 10 Years	3
Held to maturity, amortized cost	277	366
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	478
Available for sale, 1 to 5 Years	4,333
Available for sale, 6 to 10 Years	3,999
Available for sale, over 10 Years	1,576
Available-for-sale, fair value	10,386
Held to maturity, under 1 Year	161
Held to maturity, 1 to 5 Years	917
Held to maturity, 6 to 10 Years	529
Held to maturity, over 10 Years	1,111
Held to maturity, amortized cost	2,718	2,855
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,202
Available for sale, 1 to 5 Years	3,707
Available for sale, 6 to 10 Years	896
Available for sale, over 10 Years	1,807
Available-for-sale, fair value	7,612
Held to maturity, under 1 Year	376
Held to maturity, 1 to 5 Years	520
Held to maturity, 6 to 10 Years	91
Held to maturity, over 10 Years	1,160
Held to maturity, amortized cost	2,147	2,202
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	177
Available for sale, 1 to 5 Years	2,140
Available for sale, 6 to 10 Years	234
Available for sale, over 10 Years	153
Available-for-sale, fair value	2,704
Held to maturity, under 1 Year	116
Held to maturity, 1 to 5 Years	993
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	1,109	1,415
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3,233
Available for sale, 1 to 5 Years	1,691
Available for sale, 6 to 10 Years	146
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,070
Held to maturity, under 1 Year	158
Held to maturity, 1 to 5 Years	115
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	273	239
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,653
Available for sale, 1 to 5 Years	2,692
Available for sale, 6 to 10 Years	664
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,009
Held to maturity, under 1 Year	98
Held to maturity, 1 to 5 Years	119
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	217	65
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6,265
Available for sale, 1 to 5 Years	10,230
Available for sale, 6 to 10 Years	1,940
Available for sale, over 10 Years	1,960
Available-for-sale, fair value	20,395
Held to maturity, under 1 Year	748
Held to maturity, 1 to 5 Years	1,747
Held to maturity, 6 to 10 Years	91
Held to maturity, over 10 Years	1,160
Held to maturity, amortized cost	3,746	3,921
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	447
Available for sale, 1 to 5 Years	2,389
Available for sale, 6 to 10 Years	5,267
Available for sale, over 10 Years	1,923
Available-for-sale, fair value	10,026
Held to maturity, amortized cost	0	1
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	282
Available for sale, 1 to 5 Years	47
Available for sale, 6 to 10 Years	528
Available for sale, over 10 Years	2,081
Available-for-sale, fair value	2,938
Held to maturity, under 1 Year	196
Held to maturity, 1 to 5 Years	70
Held to maturity, 6 to 10 Years	302
Held to maturity, over 10 Years	989
Held to maturity, amortized cost	1,557	$ 1,687
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	837
Available for sale, 1 to 5 Years	1,224
Available for sale, 6 to 10 Years	139
Available for sale, over 10 Years	31
Available-for-sale, fair value	$ 2,231