Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 12,046	$ 22,336
Available for sale, gross unrealized losses less than 12 months	111	159
Available for sale, fair value 12 months or longer	10,356	9,468
Available for sale, gross unrealized losses 12 months or longer	345	349
Available for sale, fair value total	22,402	31,804
Available for sale, gross unrealized losses total	456	508
Held to maturity, fair value less than 12 months	4,480	20,679
Held-to-maturity, gross, less than 12 months	58	169
Held to maturity, fair value 12 months or longer	2,210	4,824
Held to maturity, gross unrealized losses 12 months or longer	62	164
Held to maturity, fair value total	6,690	25,503
Held to maturity, gross unrealized losses total	120	333
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	106	3,123
Available for sale, gross unrealized losses less than 12 months	1	4
Available for sale, fair value 12 months or longer	116	121
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	222	3,244
Available for sale, gross unrealized losses total	2	5
Held to maturity, fair value less than 12 months	781	16,370
Held-to-maturity, gross, less than 12 months	3	120
Held to maturity, fair value 12 months or longer	613	3,005
Held to maturity, gross unrealized losses 12 months or longer	3	97
Held to maturity, fair value total	1,394	19,375
Held to maturity, gross unrealized losses total	6	217
US Treasury and federal agencies, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,127	5,729
Available for sale, gross unrealized losses less than 12 months	3	48
Available for sale, fair value 12 months or longer	3,630	3,166
Available for sale, gross unrealized losses 12 months or longer	34	86
Available for sale, fair value total	4,757	8,895
Available for sale, gross unrealized losses total	37	134
Held to maturity, fair value less than 12 months	267	560
Held-to-maturity, gross, less than 12 months	0	8
Held to maturity, fair value 12 months or longer	0	0
Held to maturity, gross unrealized losses 12 months or longer	0	0
Held to maturity, fair value total	267	560
Held to maturity, gross unrealized losses total	0	8
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,886	2,841
Available for sale, gross unrealized losses less than 12 months	70	54
Available for sale, fair value 12 months or longer	3,154	3,217
Available for sale, gross unrealized losses 12 months or longer	174	144
Available for sale, fair value total	6,040	6,058
Available for sale, gross unrealized losses total	244	198
Held to maturity, fair value less than 12 months	967	896
Held-to-maturity, gross, less than 12 months	33	25
Held to maturity, fair value 12 months or longer	521	615
Held to maturity, gross unrealized losses 12 months or longer	23	22
Held to maturity, fair value total	1,488	1,511
Held to maturity, gross unrealized losses total	56	47
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	50	838
Available for sale, gross unrealized losses less than 12 months	0	7
Available for sale, fair value 12 months or longer	500	490
Available for sale, gross unrealized losses 12 months or longer	31	30
Available for sale, fair value total	550	1,328
Available for sale, gross unrealized losses total	31	37
Held to maturity, fair value less than 12 months	307	636
Held-to-maturity, gross, less than 12 months	0	1
Held to maturity, fair value 12 months or longer	0	0
Held to maturity, gross unrealized losses 12 months or longer	0	0
Held to maturity, fair value total	307	636
Held to maturity, gross unrealized losses total	0	1
Asset-backed securities, sub-prime
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1	7
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	365	387
Available for sale, gross unrealized losses 12 months or longer	34	31
Available for sale, fair value total	366	394
Available for sale, gross unrealized losses total	34	31
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,165	720
Available for sale, gross unrealized losses less than 12 months	5	3
Available for sale, fair value 12 months or longer	45	43
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	1,210	763
Available for sale, gross unrealized losses total	6	3
Held to maturity, fair value less than 12 months	161	102
Held-to-maturity, gross, less than 12 months	1	0
Held to maturity, fair value 12 months or longer	30	31
Held to maturity, gross unrealized losses 12 months or longer	0	1
Held to maturity, fair value total	191	133
Held to maturity, gross unrealized losses total	1	1
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	4,102	4,406
Available for sale, gross unrealized losses less than 12 months	75	64
Available for sale, fair value 12 months or longer	4,064	4,137
Available for sale, gross unrealized losses 12 months or longer	240	205
Available for sale, fair value total	8,166	8,543
Available for sale, gross unrealized losses total	315	269
Held to maturity, fair value less than 12 months	1,435	1,634
Held-to-maturity, gross, less than 12 months	34	26
Held to maturity, fair value 12 months or longer	551	646
Held to maturity, gross unrealized losses 12 months or longer	23	23
Held to maturity, fair value total	1,986	2,280
Held to maturity, gross unrealized losses total	57	49
Non-U.S. debt securities, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,265	1,457
Available for sale, gross unrealized losses less than 12 months	13	7
Available for sale, fair value 12 months or longer	809	437
Available for sale, gross unrealized losses 12 months or longer	13	4
Available for sale, fair value total	3,074	1,894
Available for sale, gross unrealized losses total	26	11
Held to maturity, fair value less than 12 months	249	338
Held-to-maturity, gross, less than 12 months	7	2
Held to maturity, fair value 12 months or longer	626	524
Held to maturity, gross unrealized losses 12 months or longer	24	24
Held to maturity, fair value total	875	862
Held to maturity, gross unrealized losses total	31	26
Non-U.S. debt securities, asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,656	2,190
Available for sale, gross unrealized losses less than 12 months	6	7
Available for sale, fair value 12 months or longer	250	22
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	1,906	2,212
Available for sale, gross unrealized losses total	7	7
Held to maturity, fair value less than 12 months	814	1,015
Held-to-maturity, gross, less than 12 months	3	3
Held to maturity, fair value 12 months or longer	60	69
Held to maturity, gross unrealized losses 12 months or longer	1	0
Held to maturity, fair value total	874	1,084
Held to maturity, gross unrealized losses total	4	3
Government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	657	1,691
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	657	1,691
Available for sale, gross unrealized losses total	0	0
Held to maturity, fair value less than 12 months	158	128
Held-to-maturity, gross, less than 12 months	0	1
Held to maturity, fair value 12 months or longer	0	0
Held to maturity, gross unrealized losses 12 months or longer	0	0
Held to maturity, fair value total	158	128
Held to maturity, gross unrealized losses total	0	1
Non-U.S. debt securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,499	1,548
Available for sale, gross unrealized losses less than 12 months	5	5
Available for sale, fair value 12 months or longer	401	527
Available for sale, gross unrealized losses 12 months or longer	5	7
Available for sale, fair value total	1,900	2,075
Available for sale, gross unrealized losses total	10	12
Held to maturity, fair value less than 12 months		0
Held-to-maturity, gross, less than 12 months		0
Held to maturity, fair value 12 months or longer		43
Held to maturity, gross unrealized losses 12 months or longer		0
Held to maturity, fair value total		43
Held to maturity, gross unrealized losses total		0
Total non-U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	6,077	6,886
Available for sale, gross unrealized losses less than 12 months	24	19
Available for sale, fair value 12 months or longer	1,460	986
Available for sale, gross unrealized losses 12 months or longer	19	11
Available for sale, fair value total	7,537	7,872
Available for sale, gross unrealized losses total	43	30
Held to maturity, fair value less than 12 months	1,221	1,481
Held-to-maturity, gross, less than 12 months	10	6
Held to maturity, fair value 12 months or longer	686	636
Held to maturity, gross unrealized losses 12 months or longer	25	24
Held to maturity, fair value total	1,907	2,117
Held to maturity, gross unrealized losses total	35	30
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	186	206
Available for sale, gross unrealized losses less than 12 months	1	1
Available for sale, fair value 12 months or longer	640	658
Available for sale, gross unrealized losses 12 months or longer	30	26
Available for sale, fair value total	826	864
Available for sale, gross unrealized losses total	31	27
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	343	1,511
Available for sale, gross unrealized losses less than 12 months	2	14
Available for sale, fair value 12 months or longer	282	217
Available for sale, gross unrealized losses 12 months or longer	7	8
Available for sale, fair value total	625	1,728
Available for sale, gross unrealized losses total	9	22
Held to maturity, fair value less than 12 months	776	634
Held-to-maturity, gross, less than 12 months	11	9
Held to maturity, fair value 12 months or longer	360	537
Held to maturity, gross unrealized losses 12 months or longer	11	20
Held to maturity, fair value total	1,136	1,171
Held to maturity, gross unrealized losses total	22	29
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	103	475
Available for sale, gross unrealized losses less than 12 months	5	9
Available for sale, fair value 12 months or longer	159	178
Available for sale, gross unrealized losses 12 months or longer	11	9
Available for sale, fair value total	262	653
Available for sale, gross unrealized losses total	16	18
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1	0
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	5	5
Available for sale, gross unrealized losses 12 months or longer	3	3
Available for sale, fair value total	6	5
Available for sale, gross unrealized losses total	3	$ 3
Non-U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1
Available for sale, gross unrealized losses less than 12 months	0
Available for sale, fair value 12 months or longer	0
Available for sale, gross unrealized losses 12 months or longer	0
Available for sale, fair value total	1
Available for sale, gross unrealized losses total	$ 0