Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 10,013
Available for sale, 1 to 5 Years	24,214
Available for sale, 6 to 10 Years	15,316
Available for sale, over 10 Years	19,924
Available-for-sale, fair value	69,467
Held to maturity, under 1 Year	1,100
Held to maturity, 1 to 5 Years	14,329
Held to maturity, 6 to 10 Years	10,768
Held to maturity, over 10 Years	3,755
Held to maturity, amortized cost	29,952	$ 17,723
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,000
Available for sale, 1 to 5 Years	3,223
Available for sale, 6 to 10 Years	40
Available for sale, over 10 Years	455
Available-for-sale, fair value	5,718
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	11,348
Held to maturity, 6 to 10 Years	9,440
Held to maturity, over 10 Years	90
Held to maturity, amortized cost	20,878	5,114
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	78
Available for sale, 1 to 5 Years	2,501
Available for sale, 6 to 10 Years	3,858
Available for sale, over 10 Years	11,728
Available-for-sale, fair value	18,165
Held to maturity, under 1 Year	1
Held to maturity, 1 to 5 Years	12
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	597
Held to maturity, amortized cost	610	62
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	339
Available for sale, 1 to 5 Years	3,702
Available for sale, 6 to 10 Years	2,054
Available for sale, over 10 Years	1,081
Available-for-sale, fair value	7,176
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	193
Held to maturity, 6 to 10 Years	304
Held to maturity, over 10 Years	1,095
Held to maturity, amortized cost	1,592	1,814
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2
Available for sale, 1 to 5 Years	259
Available for sale, 6 to 10 Years	1,080
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,341
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	680
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	5
Available for sale, 6 to 10 Years	3
Available for sale, over 10 Years	410
Available-for-sale, fair value	419
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	19
Available for sale, 1 to 5 Years	220
Available for sale, 6 to 10 Years	1,260
Available for sale, over 10 Years	265
Available-for-sale, fair value	1,764
Held to maturity, under 1 Year	60
Held to maturity, 1 to 5 Years	227
Held to maturity, 6 to 10 Years	76
Held to maturity, over 10 Years	3
Held to maturity, amortized cost	366	577
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	361
Available for sale, 1 to 5 Years	4,186
Available for sale, 6 to 10 Years	4,397
Available for sale, over 10 Years	1,756
Available-for-sale, fair value	10,700
Held to maturity, under 1 Year	60
Held to maturity, 1 to 5 Years	1,100
Held to maturity, 6 to 10 Years	597
Held to maturity, over 10 Years	1,098
Held to maturity, amortized cost	2,855	3,288
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,103
Available for sale, 1 to 5 Years	3,375
Available for sale, 6 to 10 Years	648
Available for sale, over 10 Years	1,945
Available-for-sale, fair value	7,071
Held to maturity, under 1 Year	435
Held to maturity, 1 to 5 Years	507
Held to maturity, 6 to 10 Years	95
Held to maturity, over 10 Years	1,165
Held to maturity, amortized cost	2,202	3,787
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	485
Available for sale, 1 to 5 Years	2,394
Available for sale, 6 to 10 Years	220
Available for sale, over 10 Years	168
Available-for-sale, fair value	3,267
Held to maturity, under 1 Year	201
Held to maturity, 1 to 5 Years	1,067
Held to maturity, 6 to 10 Years	147
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	1,415	2,868
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,736
Available for sale, 1 to 5 Years	1,619
Available for sale, 6 to 10 Years	0
Available for sale, over 10 Years	0
Available-for-sale, fair value	4,355
Held to maturity, under 1 Year	129
Held to maturity, 1 to 5 Years	110
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	239	154
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,410
Available for sale, 1 to 5 Years	2,886
Available for sale, 6 to 10 Years	538
Available for sale, over 10 Years	0
Available-for-sale, fair value	4,834
Held to maturity, under 1 Year	22
Held to maturity, 1 to 5 Years	43
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	65	72
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	5,734
Available for sale, 1 to 5 Years	10,274
Available for sale, 6 to 10 Years	1,406
Available for sale, over 10 Years	2,113
Available-for-sale, fair value	19,527
Held to maturity, under 1 Year	787
Held to maturity, 1 to 5 Years	1,727
Held to maturity, 6 to 10 Years	242
Held to maturity, over 10 Years	1,165
Held to maturity, amortized cost	3,921	6,881
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	542
Available for sale, 1 to 5 Years	2,450
Available for sale, 6 to 10 Years	5,001
Available for sale, over 10 Years	1,753
Available-for-sale, fair value	9,746
Held to maturity, under 1 Year	1
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	1	9
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	350
Available for sale, 1 to 5 Years	80
Available for sale, 6 to 10 Years	472
Available for sale, over 10 Years	2,085
Available-for-sale, fair value	2,987
Held to maturity, under 1 Year	251
Held to maturity, 1 to 5 Years	142
Held to maturity, 6 to 10 Years	489
Held to maturity, over 10 Years	805
Held to maturity, amortized cost	1,687	$ 2,369
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	948
Available for sale, 1 to 5 Years	1,500
Available for sale, 6 to 10 Years	142
Available for sale, over 10 Years	34
Available-for-sale, fair value	$ 2,624