Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 9,394	$ 22,336
Available for sale, gross unrealized losses less than 12 months	69	159
Available for sale, fair value 12 months or longer	8,926	9,468
Available for sale, gross unrealized losses 12 months or longer	299	349
Available for sale, fair value total	18,320	31,804
Available for sale, gross unrealized losses total	368	508
Held to maturity, fair value less than 12 months	2,570	20,679
Held-to-maturity, gross, less than 12 months	48	169
Held to maturity, fair value 12 months or longer	1,538	4,824
Held to maturity, gross unrealized losses 12 months or longer	58	164
Held to maturity, fair value total	4,108	25,503
Held to maturity, gross unrealized losses total	106	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	84	3,123
Available for sale, gross unrealized losses less than 12 months	0	4
Available for sale, fair value 12 months or longer	129	121
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	213	3,244
Available for sale, gross unrealized losses total	1	5
Held to maturity, fair value less than 12 months	2	16,370
Held-to-maturity, gross, less than 12 months	0	120
Held to maturity, fair value 12 months or longer	91	3,005
Held to maturity, gross unrealized losses 12 months or longer	1	97
Held to maturity, fair value total	93	19,375
Held to maturity, gross unrealized losses total	1	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	828	5,729
Available for sale, gross unrealized losses less than 12 months	2	48
Available for sale, fair value 12 months or longer	1,189	3,166
Available for sale, gross unrealized losses 12 months or longer	9	86
Available for sale, fair value total	2,017	8,895
Available for sale, gross unrealized losses total	11	134
Held to maturity, fair value less than 12 months		560
Held-to-maturity, gross, less than 12 months		8
Held to maturity, fair value 12 months or longer		0
Held to maturity, gross unrealized losses 12 months or longer		0
Held to maturity, fair value total		560
Held to maturity, gross unrealized losses total		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	2,210	2,841
Available for sale, gross unrealized losses less than 12 months	39	54
Available for sale, fair value 12 months or longer	4,049	3,217
Available for sale, gross unrealized losses 12 months or longer	177	144
Available for sale, fair value total	6,259	6,058
Available for sale, gross unrealized losses total	216	198
Held to maturity, fair value less than 12 months	809	896
Held-to-maturity, gross, less than 12 months	27	25
Held to maturity, fair value 12 months or longer	631	615
Held to maturity, gross unrealized losses 12 months or longer	24	22
Held to maturity, fair value total	1,440	1,511
Held to maturity, gross unrealized losses total	51	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	0	838
Available for sale, gross unrealized losses less than 12 months	0	7
Available for sale, fair value 12 months or longer	558	490
Available for sale, gross unrealized losses 12 months or longer	27	30
Available for sale, fair value total	558	1,328
Available for sale, gross unrealized losses total	27	37
Held to maturity, fair value less than 12 months	218	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	218	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	349	387
Available for sale, gross unrealized losses 12 months or longer	28	31
Available for sale, fair value total	350	394
Available for sale, gross unrealized losses total	28	31
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	399	720
Available for sale, gross unrealized losses less than 12 months	1	3
Available for sale, fair value 12 months or longer	25	43
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	424	763
Available for sale, gross unrealized losses total	1	3
Held to maturity, fair value less than 12 months	6	102
Held-to-maturity, gross, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	50	31
Held to maturity, gross unrealized losses 12 months or longer	0	1
Held to maturity, fair value total	56	133
Held to maturity, gross unrealized losses total	0	1
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,610	4,406
Available for sale, gross unrealized losses less than 12 months	40	64
Available for sale, fair value 12 months or longer	4,981	4,137
Available for sale, gross unrealized losses 12 months or longer	232	205
Available for sale, fair value total	7,591	8,543
Available for sale, gross unrealized losses total	272	269
Held to maturity, fair value less than 12 months	1,033	1,634
Held-to-maturity, gross, less than 12 months	27	26
Held to maturity, fair value 12 months or longer	681	646
Held to maturity, gross unrealized losses 12 months or longer	24	23
Held to maturity, fair value total	1,714	2,280
Held to maturity, gross unrealized losses total	51	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	2,825	1,457
Available for sale, gross unrealized losses less than 12 months	17	7
Available for sale, fair value 12 months or longer	757	437
Available for sale, gross unrealized losses 12 months or longer	11	4
Available for sale, fair value total	3,582	1,894
Available for sale, gross unrealized losses total	28	11
Held to maturity, fair value less than 12 months	189	338
Held-to-maturity, gross, less than 12 months	7	2
Held to maturity, fair value 12 months or longer	515	524
Held to maturity, gross unrealized losses 12 months or longer	24	24
Held to maturity, fair value total	704	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	1,276	2,190
Available for sale, gross unrealized losses less than 12 months	7	7
Available for sale, fair value 12 months or longer	233	22
Available for sale, gross unrealized losses 12 months or longer	2	0
Available for sale, fair value total	1,509	2,212
Available for sale, gross unrealized losses total	9	7
Held to maturity, fair value less than 12 months	421	1,015
Held-to-maturity, gross, less than 12 months	4	3
Held to maturity, fair value 12 months or longer	51	69
Held to maturity, gross unrealized losses 12 months or longer	0	0
Held to maturity, fair value total	472	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	486	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	486	1,691
Available for sale, gross unrealized losses total	0	0
Held to maturity, fair value less than 12 months	197	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	197	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	1,003	1,548
Available for sale, gross unrealized losses less than 12 months	2	5
Available for sale, fair value 12 months or longer	572	527
Available for sale, gross unrealized losses 12 months or longer	2	7
Available for sale, fair value total	1,575	2,075
Available for sale, gross unrealized losses total	4	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	5,590	6,886
Available for sale, gross unrealized losses less than 12 months	26	19
Available for sale, fair value 12 months or longer	1,562	986
Available for sale, gross unrealized losses 12 months or longer	15	11
Available for sale, fair value total	7,152	7,872
Available for sale, gross unrealized losses total	41	30
Held to maturity, fair value less than 12 months	807	1,481
Held-to-maturity, gross, less than 12 months	11	6
Held to maturity, fair value 12 months or longer	566	636
Held to maturity, gross unrealized losses 12 months or longer	24	24
Held to maturity, fair value total	1,373	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	102	206
Available for sale, gross unrealized losses less than 12 months	0	1
Available for sale, fair value 12 months or longer	612	658
Available for sale, gross unrealized losses 12 months or longer	25	26
Available for sale, fair value total	714	864
Available for sale, gross unrealized losses total	25	27
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	128	1,511
Available for sale, gross unrealized losses less than 12 months	1	14
Available for sale, fair value 12 months or longer	282	217
Available for sale, gross unrealized losses 12 months or longer	5	8
Available for sale, fair value total	410	1,728
Available for sale, gross unrealized losses total	6	22
Held to maturity, fair value less than 12 months	728	634
Held-to-maturity, gross, less than 12 months	10	9
Held to maturity, fair value 12 months or longer	200	537
Held to maturity, gross unrealized losses 12 months or longer	9	20
Held to maturity, fair value total	928	1,171
Held to maturity, gross unrealized losses total	19	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	51	475
Available for sale, gross unrealized losses less than 12 months	0	9
Available for sale, fair value 12 months or longer	166	178
Available for sale, gross unrealized losses 12 months or longer	9	9
Available for sale, fair value total	217	653
Available for sale, gross unrealized losses total	9	18
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	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	5	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