Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 11,823
Available for sale, 1 to 5 Years	19,415
Available for sale, 6 to 10 Years	14,486
Available for sale, over 10 Years	12,600
Available-for-sale, fair value	58,324
Held to maturity, under 1 Year	1,641
Held to maturity, 1 to 5 Years	18,146
Held to maturity, 6 to 10 Years	3,270
Held to maturity, over 10 Years	12,772
Held to maturity, amortized cost	35,829	$ 35,169
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,731
Available for sale, 1 to 5 Years	11
Available for sale, 6 to 10 Years	44
Available for sale, over 10 Years	365
Available-for-sale, fair value	3,151
Held to maturity, under 1 Year	400
Held to maturity, 1 to 5 Years	16,319
Held to maturity, 6 to 10 Years	716
Held to maturity, over 10 Years	69
Held to maturity, amortized cost	17,504	17,527
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	224
Available for sale, 1 to 5 Years	1,433
Available for sale, 6 to 10 Years	3,235
Available for sale, over 10 Years	6,456
Available-for-sale, fair value	11,348
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	180
Held to maturity, 6 to 10 Years	1,724
Held to maturity, over 10 Years	9,350
Held to maturity, amortized cost	11,254	10,334
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	580
Available for sale, 1 to 5 Years	3,038
Available for sale, 6 to 10 Years	807
Available for sale, over 10 Years	1,266
Available-for-sale, fair value	5,691
Held to maturity, under 1 Year	348
Held to maturity, 1 to 5 Years	231
Held to maturity, 6 to 10 Years	293
Held to maturity, over 10 Years	1,940
Held to maturity, amortized cost	2,812	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	1,005
Available for sale, 6 to 10 Years	297
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,302
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	1
Available for sale, 1 to 5 Years	2
Available for sale, 6 to 10 Years	2
Available for sale, over 10 Years	247
Available-for-sale, fair value	252
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	62
Available for sale, 6 to 10 Years	809
Available for sale, over 10 Years	0
Available-for-sale, fair value	871
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	2
Held to maturity, amortized cost	15	35
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	581
Available for sale, 1 to 5 Years	4,107
Available for sale, 6 to 10 Years	1,915
Available for sale, over 10 Years	1,513
Available-for-sale, fair value	8,116
Held to maturity, under 1 Year	473
Held to maturity, 1 to 5 Years	977
Held to maturity, 6 to 10 Years	293
Held to maturity, over 10 Years	1,942
Held to maturity, amortized cost	3,685	3,815
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,213
Available for sale, 1 to 5 Years	3,643
Available for sale, 6 to 10 Years	831
Available for sale, over 10 Years	896
Available-for-sale, fair value	6,583
Held to maturity, under 1 Year	249
Held to maturity, 1 to 5 Years	232
Held to maturity, 6 to 10 Years	55
Held to maturity, over 10 Years	595
Held to maturity, amortized cost	1,131	1,150
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	260
Available for sale, 1 to 5 Years	2,281
Available for sale, 6 to 10 Years	268
Available for sale, over 10 Years	2
Available-for-sale, fair value	2,811
Held to maturity, under 1 Year	168
Held to maturity, 1 to 5 Years	269
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	437	531
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,079
Available for sale, 1 to 5 Years	999
Available for sale, 6 to 10 Years	726
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,804
Held to maturity, under 1 Year	232
Held to maturity, 1 to 5 Years	108
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	340	286
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,837
Available for sale, 1 to 5 Years	3,465
Available for sale, 6 to 10 Years	500
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,802
Held to maturity, under 1 Year	74
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	117	113
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	7,389
Available for sale, 1 to 5 Years	10,388
Available for sale, 6 to 10 Years	2,325
Available for sale, over 10 Years	898
Available-for-sale, fair value	21,000
Held to maturity, under 1 Year	723
Held to maturity, 1 to 5 Years	652
Held to maturity, 6 to 10 Years	55
Held to maturity, over 10 Years	595
Held to maturity, amortized cost	2,025	2,080
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	492
Available for sale, 1 to 5 Years	2,379
Available for sale, 6 to 10 Years	5,161
Available for sale, over 10 Years	1,790
Available-for-sale, fair value	9,822
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	64
Available for sale, 6 to 10 Years	828
Available for sale, over 10 Years	1,569
Available-for-sale, fair value	2,461
Held to maturity, under 1 Year	45
Held to maturity, 1 to 5 Years	18
Held to maturity, 6 to 10 Years	482
Held to maturity, over 10 Years	816
Held to maturity, amortized cost	1,361	$ 1,413
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	406
Available for sale, 1 to 5 Years	1,033
Available for sale, 6 to 10 Years	978
Available for sale, over 10 Years	9
Available-for-sale, fair value	$ 2,426