Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 9,001
Available for sale, 1 to 5 Years	20,551
Available for sale, 6 to 10 Years	16,233
Available for sale, over 10 Years	13,117
Available-for-sale, fair value	58,902
Held to maturity, under 1 Year	2,305
Held to maturity, 1 to 5 Years	17,622
Held to maturity, 6 to 10 Years	2,625
Held to maturity, over 10 Years	13,678
Held to maturity, amortized cost	36,230	$ 35,169
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	231
Available for sale, 1 to 5 Years	8
Available for sale, 6 to 10 Years	52
Available for sale, over 10 Years	342
Available-for-sale, fair value	633
Held to maturity, under 1 Year	1,199
Held to maturity, 1 to 5 Years	15,800
Held to maturity, 6 to 10 Years	414
Held to maturity, over 10 Years	66
Held to maturity, amortized cost	17,479	17,527
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	254
Available for sale, 1 to 5 Years	1,463
Available for sale, 6 to 10 Years	3,241
Available for sale, over 10 Years	6,456
Available-for-sale, fair value	11,414
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	182
Held to maturity, 6 to 10 Years	1,386
Held to maturity, over 10 Years	10,369
Held to maturity, amortized cost	11,937	10,334
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	915
Available for sale, 1 to 5 Years	2,415
Available for sale, 6 to 10 Years	894
Available for sale, over 10 Years	1,663
Available-for-sale, fair value	5,887
Held to maturity, under 1 Year	307
Held to maturity, 1 to 5 Years	246
Held to maturity, 6 to 10 Years	291
Held to maturity, over 10 Years	1,894
Held to maturity, amortized cost	2,738	2,883
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	1,006
Available for sale, 6 to 10 Years	550
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,556
Held to maturity, under 1 Year	124
Held to maturity, 1 to 5 Years	734
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	858	897
Asset-backed securities, sub-prime
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	2
Available for sale, 6 to 10 Years	2
Available for sale, over 10 Years	239
Available-for-sale, fair value	243
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	122
Available for sale, 6 to 10 Years	1,038
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,160
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	4
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	1
Held to maturity, amortized cost	5	35
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	915
Available for sale, 1 to 5 Years	3,545
Available for sale, 6 to 10 Years	2,484
Available for sale, over 10 Years	1,902
Available-for-sale, fair value	8,846
Held to maturity, under 1 Year	431
Held to maturity, 1 to 5 Years	984
Held to maturity, 6 to 10 Years	291
Held to maturity, over 10 Years	1,895
Held to maturity, amortized cost	3,601	3,815
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,152
Available for sale, 1 to 5 Years	3,909
Available for sale, 6 to 10 Years	964
Available for sale, over 10 Years	937
Available-for-sale, fair value	6,962
Held to maturity, under 1 Year	223
Held to maturity, 1 to 5 Years	242
Held to maturity, 6 to 10 Years	51
Held to maturity, over 10 Years	568
Held to maturity, amortized cost	1,084	1,150
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	370
Available for sale, 1 to 5 Years	2,261
Available for sale, 6 to 10 Years	260
Available for sale, over 10 Years	0
Available-for-sale, fair value	2,891
Held to maturity, under 1 Year	127
Held to maturity, 1 to 5 Years	238
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	365	531
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3,144
Available for sale, 1 to 5 Years	2,255
Available for sale, 6 to 10 Years	1,201
Available for sale, over 10 Years	0
Available-for-sale, fair value	6,600
Held to maturity, under 1 Year	242
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	357	286
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,030
Available for sale, 1 to 5 Years	3,535
Available for sale, 6 to 10 Years	711
Available for sale, over 10 Years	0
Available-for-sale, fair value	6,276
Held to maturity, under 1 Year	76
Held to maturity, 1 to 5 Years	46
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	122	113
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6,696
Available for sale, 1 to 5 Years	11,960
Available for sale, 6 to 10 Years	3,136
Available for sale, over 10 Years	937
Available-for-sale, fair value	22,729
Held to maturity, under 1 Year	668
Held to maturity, 1 to 5 Years	641
Held to maturity, 6 to 10 Years	51
Held to maturity, over 10 Years	568
Held to maturity, amortized cost	1,928	2,080
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	398
Available for sale, 1 to 5 Years	2,493
Available for sale, 6 to 10 Years	5,181
Available for sale, over 10 Years	1,966
Available-for-sale, fair value	10,038
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	158
Available for sale, 6 to 10 Years	771
Available for sale, over 10 Years	1,514
Available-for-sale, fair value	2,443
Held to maturity, under 1 Year	7
Held to maturity, 1 to 5 Years	15
Held to maturity, 6 to 10 Years	483
Held to maturity, over 10 Years	780
Held to maturity, amortized cost	1,285	$ 1,413
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	507
Available for sale, 1 to 5 Years	924
Available for sale, 6 to 10 Years	1,368
Available for sale, over 10 Years	0
Available-for-sale, fair value	$ 2,799