Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 8,382	$ 22,336
Available for sale, gross unrealized losses less than 12 months	30	159
Available for sale, fair value 12 months or longer	9,863	9,468
Available for sale, gross unrealized losses 12 months or longer	261	349
Available for sale, fair value total	18,245	31,804
Available for sale, gross unrealized losses total	291	508
Held to maturity, fair value less than 12 months	2,195	20,679
Held-to-maturity, gross, less than 12 months	22	169
Held to maturity, fair value 12 months or longer	1,900	4,824
Held to maturity, gross unrealized losses 12 months or longer	53	164
Held to maturity, fair value total	4,095	25,503
Held to maturity, gross unrealized losses total	75	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	35	3,123
Available for sale, gross unrealized losses less than 12 months	0	4
Available for sale, fair value 12 months or longer	177	121
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	212	3,244
Available for sale, gross unrealized losses total	1	5
Held to maturity, fair value less than 12 months	0	16,370
Held-to-maturity, gross, less than 12 months	0	120
Held to maturity, fair value 12 months or longer	90	3,005
Held to maturity, gross unrealized losses 12 months or longer	1	97
Held to maturity, fair value total	90	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	3,116	5,729
Available for sale, gross unrealized losses less than 12 months	12	48
Available for sale, fair value 12 months or longer	858	3,166
Available for sale, gross unrealized losses 12 months or longer	13	86
Available for sale, fair value total	3,974	8,895
Available for sale, gross unrealized losses total	25	134
Held to maturity, fair value less than 12 months	936	560
Held-to-maturity, gross, less than 12 months	3	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	936	560
Held to maturity, gross unrealized losses total	3	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	520	2,841
Available for sale, gross unrealized losses less than 12 months	3	54
Available for sale, fair value 12 months or longer	4,990	3,217
Available for sale, gross unrealized losses 12 months or longer	160	144
Available for sale, fair value total	5,510	6,058
Available for sale, gross unrealized losses total	163	198
Held to maturity, fair value less than 12 months	452	896
Held-to-maturity, gross, less than 12 months	12	25
Held to maturity, fair value 12 months or longer	922	615
Held to maturity, gross unrealized losses 12 months or longer	28	22
Held to maturity, fair value total	1,374	1,511
Held to maturity, gross unrealized losses total	40	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	505	490
Available for sale, gross unrealized losses 12 months or longer	25	30
Available for sale, fair value total	505	1,328
Available for sale, gross unrealized losses total	25	37
Held to maturity, fair value less than 12 months		636
Held-to-maturity, gross, less than 12 months		1
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		636
Held to maturity, gross unrealized losses total		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	3	7
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	330	387
Available for sale, gross unrealized losses 12 months or longer	24	31
Available for sale, fair value total	333	394
Available for sale, gross unrealized losses total	24	31
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	150	720
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	150	43
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	300	763
Available for sale, gross unrealized losses total	0	3
Held to maturity, fair value less than 12 months	0	102
Held-to-maturity, gross, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	15	31
Held to maturity, gross unrealized losses 12 months or longer	0	1
Held to maturity, fair value total	15	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	673	4,406
Available for sale, gross unrealized losses less than 12 months	3	64
Available for sale, fair value 12 months or longer	5,975	4,137
Available for sale, gross unrealized losses 12 months or longer	209	205
Available for sale, fair value total	6,648	8,543
Available for sale, gross unrealized losses total	212	269
Held to maturity, fair value less than 12 months	452	1,634
Held-to-maturity, gross, less than 12 months	12	26
Held to maturity, fair value 12 months or longer	937	646
Held to maturity, gross unrealized losses 12 months or longer	28	23
Held to maturity, fair value total	1,389	2,280
Held to maturity, gross unrealized losses total	40	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	368	1,457
Available for sale, gross unrealized losses less than 12 months	1	7
Available for sale, fair value 12 months or longer	1,137	437
Available for sale, gross unrealized losses 12 months or longer	8	4
Available for sale, fair value total	1,505	1,894
Available for sale, gross unrealized losses total	9	11
Held to maturity, fair value less than 12 months	104	338
Held-to-maturity, gross, less than 12 months	3	2
Held to maturity, fair value 12 months or longer	406	524
Held to maturity, gross unrealized losses 12 months or longer	14	24
Held to maturity, fair value total	510	862
Held to maturity, gross unrealized losses total	17	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	333	2,190
Available for sale, gross unrealized losses less than 12 months	1	7
Available for sale, fair value 12 months or longer	463	22
Available for sale, gross unrealized losses 12 months or longer	2	0
Available for sale, fair value total	796	2,212
Available for sale, gross unrealized losses total	3	7
Held to maturity, fair value less than 12 months	8	1,015
Held-to-maturity, gross, less than 12 months	0	3
Held to maturity, fair value 12 months or longer	271	69
Held to maturity, gross unrealized losses 12 months or longer	1	0
Held to maturity, fair value total	279	1,084
Held to maturity, gross unrealized losses total	1	3
Government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,044	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	2,044	1,691
Available for sale, gross unrealized losses total	0	0
Held to maturity, fair value less than 12 months	174	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	174	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	569	1,548
Available for sale, gross unrealized losses less than 12 months	1	5
Available for sale, fair value 12 months or longer	363	527
Available for sale, gross unrealized losses 12 months or longer	0	7
Available for sale, fair value total	932	2,075
Available for sale, gross unrealized losses total	1	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	3,314	6,886
Available for sale, gross unrealized losses less than 12 months	3	19
Available for sale, fair value 12 months or longer	1,963	986
Available for sale, gross unrealized losses 12 months or longer	10	11
Available for sale, fair value total	5,277	7,872
Available for sale, gross unrealized losses total	13	30
Held to maturity, fair value less than 12 months	286	1,481
Held-to-maturity, gross, less than 12 months	3	6
Held to maturity, fair value 12 months or longer	677	636
Held to maturity, gross unrealized losses 12 months or longer	15	24
Held to maturity, fair value total	963	2,117
Held to maturity, gross unrealized losses total	18	30
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	714	206
Available for sale, gross unrealized losses less than 12 months	9	1
Available for sale, fair value 12 months or longer	508	658
Available for sale, gross unrealized losses 12 months or longer	14	26
Available for sale, fair value total	1,222	864
Available for sale, gross unrealized losses total	23	27
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	397	1,511
Available for sale, gross unrealized losses less than 12 months	3	14
Available for sale, fair value 12 months or longer	219	217
Available for sale, gross unrealized losses 12 months or longer	5	8
Available for sale, fair value total	616	1,728
Available for sale, gross unrealized losses total	8	22
Held to maturity, fair value less than 12 months	521	634
Held-to-maturity, gross, less than 12 months	4	9
Held to maturity, fair value 12 months or longer	196	537
Held to maturity, gross unrealized losses 12 months or longer	9	20
Held to maturity, fair value total	717	1,171
Held to maturity, gross unrealized losses total	13	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	133	475
Available for sale, gross unrealized losses less than 12 months	0	9
Available for sale, fair value 12 months or longer	157	178
Available for sale, gross unrealized losses 12 months or longer	7	9
Available for sale, fair value total	290	653
Available for sale, gross unrealized losses total	7	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	2	3
Available for sale, fair value total	5	5
Available for sale, gross unrealized losses total	2	$ 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	0
Available for sale, gross unrealized losses less than 12 months	0
Available for sale, fair value 12 months or longer	1
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