Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 12,415
Available for sale, 1 to 5 Years	19,803
Available for sale, 6 to 10 Years	14,306
Available for sale, over 10 Years	15,004
Available-for-sale, fair value	61,528
Held to maturity, under 1 Year	1,612
Held to maturity, 1 to 5 Years	16,976
Held to maturity, 6 to 10 Years	4,595
Held to maturity, over 10 Years	11,986
Held to maturity, amortized cost	35,169	$ 29,952
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2,722
Available for sale, 1 to 5 Years	1,114
Available for sale, 6 to 10 Years	44
Available for sale, over 10 Years	383
Available-for-sale, fair value	4,263
Held to maturity, under 1 Year	400
Held to maturity, 1 to 5 Years	14,888
Held to maturity, 6 to 10 Years	2,167
Held to maturity, over 10 Years	72
Held to maturity, amortized cost	17,527	20,878
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	213
Available for sale, 1 to 5 Years	1,533
Available for sale, 6 to 10 Years	3,022
Available for sale, over 10 Years	8,489
Available-for-sale, fair value	13,257
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	193
Held to maturity, 6 to 10 Years	1,536
Held to maturity, over 10 Years	8,605
Held to maturity, amortized cost	10,334	610
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	590
Available for sale, 1 to 5 Years	3,181
Available for sale, 6 to 10 Years	757
Available for sale, over 10 Years	1,068
Available-for-sale, fair value	5,596
Held to maturity, under 1 Year	442
Held to maturity, 1 to 5 Years	201
Held to maturity, 6 to 10 Years	349
Held to maturity, over 10 Years	1,891
Held to maturity, amortized cost	2,883	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	1,052
Available for sale, 6 to 10 Years	295
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,351
Held to maturity, under 1 Year	99
Held to maturity, 1 to 5 Years	798
Held to maturity, 6 to 10 Years	0
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	1
Available for sale, 6 to 10 Years	2
Available for sale, over 10 Years	266
Available-for-sale, fair value	272
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1
Available for sale, 1 to 5 Years	21
Available for sale, 6 to 10 Years	883
Available for sale, over 10 Years	0
Available-for-sale, fair value	905
Held to maturity, under 1 Year	7
Held to maturity, 1 to 5 Years	18
Held to maturity, 6 to 10 Years	8
Held to maturity, over 10 Years	2
Held to maturity, amortized cost	35	366
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	598
Available for sale, 1 to 5 Years	4,255
Available for sale, 6 to 10 Years	1,937
Available for sale, over 10 Years	1,334
Available-for-sale, fair value	8,124
Held to maturity, under 1 Year	548
Held to maturity, 1 to 5 Years	1,017
Held to maturity, 6 to 10 Years	357
Held to maturity, over 10 Years	1,893
Held to maturity, amortized cost	3,815	2,855
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,301
Available for sale, 1 to 5 Years	3,339
Available for sale, 6 to 10 Years	731
Available for sale, over 10 Years	1,164
Available-for-sale, fair value	6,535
Held to maturity, under 1 Year	148
Held to maturity, 1 to 5 Years	339
Held to maturity, 6 to 10 Years	47
Held to maturity, over 10 Years	616
Held to maturity, amortized cost	1,150	2,202
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	289
Available for sale, 1 to 5 Years	1,877
Available for sale, 6 to 10 Years	346
Available for sale, over 10 Years	4
Available-for-sale, fair value	2,516
Held to maturity, under 1 Year	163
Held to maturity, 1 to 5 Years	368
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	531	1,415
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,372
Available for sale, 1 to 5 Years	987
Available for sale, 6 to 10 Years	477
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,836
Held to maturity, under 1 Year	180
Held to maturity, 1 to 5 Years	106
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	286	239
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,901
Available for sale, 1 to 5 Years	3,304
Available for sale, 6 to 10 Years	408
Available for sale, over 10 Years	0
Available-for-sale, fair value	5,613
Held to maturity, under 1 Year	71
Held to maturity, 1 to 5 Years	42
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	113	65
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	7,863
Available for sale, 1 to 5 Years	9,507
Available for sale, 6 to 10 Years	1,962
Available for sale, over 10 Years	1,168
Available-for-sale, fair value	20,500
Held to maturity, under 1 Year	562
Held to maturity, 1 to 5 Years	855
Held to maturity, 6 to 10 Years	47
Held to maturity, over 10 Years	616
Held to maturity, amortized cost	2,080	3,921
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	509
Available for sale, 1 to 5 Years	2,347
Available for sale, 6 to 10 Years	5,548
Available for sale, over 10 Years	1,918
Available-for-sale, fair value	10,322
Held to maturity, amortized cost	0	1
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	2
Available for sale, 1 to 5 Years	44
Available for sale, 6 to 10 Years	871
Available for sale, over 10 Years	1,676
Available-for-sale, fair value	2,593
Held to maturity, under 1 Year	102
Held to maturity, 1 to 5 Years	23
Held to maturity, 6 to 10 Years	488
Held to maturity, over 10 Years	800
Held to maturity, amortized cost	1,413	$ 1,687
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	508
Available for sale, 1 to 5 Years	1,003
Available for sale, 6 to 10 Years	922
Available for sale, over 10 Years	36
Available-for-sale, fair value	$ 2,469