Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 16,928	$ 22,336
Available for sale, gross unrealized losses less than 12 months	308	159
Available for sale, fair value 12 months or longer	7,800	9,468
Available for sale, gross unrealized losses 12 months or longer	177	349
Available for sale, fair value total	24,728	31,804
Available for sale, gross unrealized losses total	485	508
Held to maturity, fair value less than 12 months	17,284	20,679
Held-to-maturity, gross, less than 12 months	293	169
Held to maturity, fair value 12 months or longer	1,899	4,824
Held to maturity, gross unrealized losses 12 months or longer	42	164
Held to maturity, fair value total	19,183	25,503
Held to maturity, gross unrealized losses total	335	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	651	3,123
Available for sale, gross unrealized losses less than 12 months	8	4
Available for sale, fair value 12 months or longer	180	121
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	831	3,244
Available for sale, gross unrealized losses total	9	5
Held to maturity, fair value less than 12 months	8,891	16,370
Held-to-maturity, gross, less than 12 months	57	120
Held to maturity, fair value 12 months or longer	86	3,005
Held to maturity, gross unrealized losses 12 months or longer	1	97
Held to maturity, fair value total	8,977	19,375
Held to maturity, gross unrealized losses total	58	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	7,072	5,729
Available for sale, gross unrealized losses less than 12 months	131	48
Available for sale, fair value 12 months or longer	1,114	3,166
Available for sale, gross unrealized losses 12 months or longer	28	86
Available for sale, fair value total	8,186	8,895
Available for sale, gross unrealized losses total	159	134
Held to maturity, fair value less than 12 months	6,838	560
Held-to-maturity, gross, less than 12 months	221	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	6,838	560
Held to maturity, gross unrealized losses total	221	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	54	2,841
Available for sale, gross unrealized losses less than 12 months	0	54
Available for sale, fair value 12 months or longer	3,745	3,217
Available for sale, gross unrealized losses 12 months or longer	75	144
Available for sale, fair value total	3,799	6,058
Available for sale, gross unrealized losses total	75	198
Held to maturity, fair value less than 12 months	705	896
Held-to-maturity, gross, less than 12 months	9	25
Held to maturity, fair value 12 months or longer	1,235	615
Held to maturity, gross unrealized losses 12 months or longer	21	22
Held to maturity, fair value total	1,940	1,511
Held to maturity, gross unrealized losses total	30	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	795	838
Available for sale, gross unrealized losses less than 12 months	1	7
Available for sale, fair value 12 months or longer	494	490
Available for sale, gross unrealized losses 12 months or longer	25	30
Available for sale, fair value total	1,289	1,328
Available for sale, gross unrealized losses total	26	37
Held to maturity, fair value less than 12 months	33	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	33	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	252	387
Available for sale, gross unrealized losses 12 months or longer	18	31
Available for sale, fair value total	253	394
Available for sale, gross unrealized losses total	18	31
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	75	720
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	0	43
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	75	763
Available for sale, gross unrealized losses total	0	3
Held to maturity, fair value less than 12 months	18	102
Held-to-maturity, gross, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	9	31
Held to maturity, gross unrealized losses 12 months or longer	0	1
Held to maturity, fair value total	27	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	925	4,406
Available for sale, gross unrealized losses less than 12 months	1	64
Available for sale, fair value 12 months or longer	4,491	4,137
Available for sale, gross unrealized losses 12 months or longer	118	205
Available for sale, fair value total	5,416	8,543
Available for sale, gross unrealized losses total	119	269
Held to maturity, fair value less than 12 months	756	1,634
Held-to-maturity, gross, less than 12 months	9	26
Held to maturity, fair value 12 months or longer	1,244	646
Held to maturity, gross unrealized losses 12 months or longer	21	23
Held to maturity, fair value total	2,000	2,280
Held to maturity, gross unrealized losses total	30	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	442	1,457
Available for sale, gross unrealized losses less than 12 months	1	7
Available for sale, fair value 12 months or longer	893	437
Available for sale, gross unrealized losses 12 months or longer	5	4
Available for sale, fair value total	1,335	1,894
Available for sale, gross unrealized losses total	6	11
Held to maturity, fair value less than 12 months	54	338
Held-to-maturity, gross, less than 12 months	2	2
Held to maturity, fair value 12 months or longer	330	524
Held to maturity, gross unrealized losses 12 months or longer	13	24
Held to maturity, fair value total	384	862
Held to maturity, gross unrealized losses total	15	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	253	2,190
Available for sale, gross unrealized losses less than 12 months	0	7
Available for sale, fair value 12 months or longer	276	22
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	529	2,212
Available for sale, gross unrealized losses total	1	7
Held to maturity, fair value less than 12 months	28	1,015
Held-to-maturity, gross, less than 12 months	0	3
Held to maturity, fair value 12 months or longer	35	69
Held to maturity, gross unrealized losses 12 months or longer	0	0
Held to maturity, fair value total	63	1,084
Held to maturity, gross unrealized losses total	0	3
Government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,314	1,691
Available for sale, gross unrealized losses less than 12 months	6	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	1,314	1,691
Available for sale, gross unrealized losses total	6	0
Held to maturity, fair value less than 12 months	180	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	180	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	670	1,548
Available for sale, gross unrealized losses less than 12 months	4	5
Available for sale, fair value 12 months or longer	218	527
Available for sale, gross unrealized losses 12 months or longer	1	7
Available for sale, fair value total	888	2,075
Available for sale, gross unrealized losses total	5	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	2,679	6,886
Available for sale, gross unrealized losses less than 12 months	11	19
Available for sale, fair value 12 months or longer	1,387	986
Available for sale, gross unrealized losses 12 months or longer	7	11
Available for sale, fair value total	4,066	7,872
Available for sale, gross unrealized losses total	18	30
Held to maturity, fair value less than 12 months	262	1,481
Held-to-maturity, gross, less than 12 months	2	6
Held to maturity, fair value 12 months or longer	365	636
Held to maturity, gross unrealized losses 12 months or longer	13	24
Held to maturity, fair value total	627	2,117
Held to maturity, gross unrealized losses total	15	30
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	3,390	206
Available for sale, gross unrealized losses less than 12 months	102	1
Available for sale, fair value 12 months or longer	304	658
Available for sale, gross unrealized losses 12 months or longer	10	26
Available for sale, fair value total	3,694	864
Available for sale, gross unrealized losses total	112	27
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,259	1,511
Available for sale, gross unrealized losses less than 12 months	31	14
Available for sale, fair value 12 months or longer	162	217
Available for sale, gross unrealized losses 12 months or longer	4	8
Available for sale, fair value total	1,421	1,728
Available for sale, gross unrealized losses total	35	22
Held to maturity, fair value less than 12 months	537	634
Held-to-maturity, gross, less than 12 months	4	9
Held to maturity, fair value 12 months or longer	204	537
Held to maturity, gross unrealized losses 12 months or longer	7	20
Held to maturity, fair value total	741	1,171
Held to maturity, gross unrealized losses total	11	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	944	475
Available for sale, gross unrealized losses less than 12 months	24	9
Available for sale, fair value 12 months or longer	157	178
Available for sale, gross unrealized losses 12 months or longer	6	9
Available for sale, fair value total	1,101	653
Available for sale, gross unrealized losses total	30	18
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	8	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	13	5
Available for sale, gross unrealized losses total	$ 3	$ 3