Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 14,679	$ 16,928
Available for sale, gross unrealized losses less than 12 months	230	308
Available for sale, fair value 12 months or longer	5,959	7,800
Available for sale, gross unrealized losses 12 months or longer	101	177
Available for sale, fair value total	20,638	24,728
Available for sale, gross unrealized losses total	331	485
Held to maturity, fair value less than 12 months	16,239	17,284
Held-to-maturity, gross, less than 12 months	281	293
Held to maturity, fair value 12 months or longer	1,612	1,899
Held to maturity, gross unrealized losses 12 months or longer	34	42
Held to maturity, fair value total	17,851	19,183
Held to maturity, gross unrealized losses total	315	335
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	663	651
Available for sale, gross unrealized losses less than 12 months	0	8
Available for sale, fair value 12 months or longer	178	180
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	841	831
Available for sale, gross unrealized losses total	1	9
Held to maturity, fair value less than 12 months	7,977	8,891
Held-to-maturity, gross, less than 12 months	43	57
Held to maturity, fair value 12 months or longer	83	86
Held to maturity, gross unrealized losses 12 months or longer	1	1
Held to maturity, fair value total	8,060	8,977
Held to maturity, gross unrealized losses total	44	58
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	5,653	7,072
Available for sale, gross unrealized losses less than 12 months	93	131
Available for sale, fair value 12 months or longer	525	1,114
Available for sale, gross unrealized losses 12 months or longer	9	28
Available for sale, fair value total	6,178	8,186
Available for sale, gross unrealized losses total	102	159
Held to maturity, fair value less than 12 months	7,240	6,838
Held-to-maturity, gross, less than 12 months	229	221
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	7,240	6,838
Held to maturity, gross unrealized losses total	229	221
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	136	54
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	3,107	3,745
Available for sale, gross unrealized losses 12 months or longer	37	75
Available for sale, fair value total	3,243	3,799
Available for sale, gross unrealized losses total	37	75
Held to maturity, fair value less than 12 months	557	705
Held-to-maturity, gross, less than 12 months	6	9
Held to maturity, fair value 12 months or longer	1,016	1,235
Held to maturity, gross unrealized losses 12 months or longer	14	21
Held to maturity, fair value total	1,573	1,940
Held to maturity, gross unrealized losses total	20	30
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	795
Available for sale, gross unrealized losses less than 12 months	0	1
Available for sale, fair value 12 months or longer	497	494
Available for sale, gross unrealized losses 12 months or longer	22	25
Available for sale, fair value total	497	1,289
Available for sale, gross unrealized losses total	22	26
Held to maturity, fair value less than 12 months		33
Held-to-maturity, gross, less than 12 months		0
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		33
Held to maturity, gross unrealized losses total		0
Asset-backed securities, sub-prime
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	1
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	233	252
Available for sale, gross unrealized losses 12 months or longer	14	18
Available for sale, fair value total	233	253
Available for sale, gross unrealized losses total	14	18
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		75
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		75
Available for sale, gross unrealized losses total		0
Held to maturity, fair value less than 12 months		18
Held-to-maturity, gross, less than 12 months		0
Held to maturity, fair value 12 months or longer		9
Held to maturity, gross unrealized losses 12 months or longer		0
Held to maturity, fair value total		27
Held to maturity, gross unrealized losses total		0
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	136	925
Available for sale, gross unrealized losses less than 12 months	0	1
Available for sale, fair value 12 months or longer	3,837	4,491
Available for sale, gross unrealized losses 12 months or longer	73	118
Available for sale, fair value total	3,973	5,416
Available for sale, gross unrealized losses total	73	119
Held to maturity, fair value less than 12 months	557	756
Held-to-maturity, gross, less than 12 months	6	9
Held to maturity, fair value 12 months or longer	1,016	1,244
Held to maturity, gross unrealized losses 12 months or longer	14	21
Held to maturity, fair value total	1,573	2,000
Held to maturity, gross unrealized losses total	20	30
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	542	442
Available for sale, gross unrealized losses less than 12 months	1	1
Available for sale, fair value 12 months or longer	780	893
Available for sale, gross unrealized losses 12 months or longer	4	5
Available for sale, fair value total	1,322	1,335
Available for sale, gross unrealized losses total	5	6
Held to maturity, fair value less than 12 months	13	54
Held-to-maturity, gross, less than 12 months	0	2
Held to maturity, fair value 12 months or longer	323	330
Held to maturity, gross unrealized losses 12 months or longer	12	13
Held to maturity, fair value total	336	384
Held to maturity, gross unrealized losses total	12	15
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	75	253
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	135	276
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	210	529
Available for sale, gross unrealized losses total	1	1
Held to maturity, fair value less than 12 months		28
Held-to-maturity, gross, less than 12 months		0
Held to maturity, fair value 12 months or longer		35
Held to maturity, gross unrealized losses 12 months or longer		0
Held to maturity, fair value total		63
Held to maturity, gross unrealized losses total		0
Government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,695	1,314
Available for sale, gross unrealized losses less than 12 months	13	6
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	2,695	1,314
Available for sale, gross unrealized losses total	13	6
Held to maturity, fair value less than 12 months		180
Held-to-maturity, gross, less than 12 months		0
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		180
Held to maturity, gross unrealized losses total		0
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	633	670
Available for sale, gross unrealized losses less than 12 months	5	4
Available for sale, fair value 12 months or longer	111	218
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	744	888
Available for sale, gross unrealized losses total	5	5
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	3,945	2,679
Available for sale, gross unrealized losses less than 12 months	19	11
Available for sale, fair value 12 months or longer	1,026	1,387
Available for sale, gross unrealized losses 12 months or longer	5	7
Available for sale, fair value total	4,971	4,066
Available for sale, gross unrealized losses total	24	18
Held to maturity, fair value less than 12 months	13	262
Held-to-maturity, gross, less than 12 months	0	2
Held to maturity, fair value 12 months or longer	323	365
Held to maturity, gross unrealized losses 12 months or longer	12	13
Held to maturity, fair value total	336	627
Held to maturity, gross unrealized losses total	12	15
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,294	3,390
Available for sale, gross unrealized losses less than 12 months	69	102
Available for sale, fair value 12 months or longer	52	304
Available for sale, gross unrealized losses 12 months or longer	1	10
Available for sale, fair value total	2,346	3,694
Available for sale, gross unrealized losses total	70	112
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,100	1,259
Available for sale, gross unrealized losses less than 12 months	30	31
Available for sale, fair value 12 months or longer	177	162
Available for sale, gross unrealized losses 12 months or longer	4	4
Available for sale, fair value total	1,277	1,421
Available for sale, gross unrealized losses total	34	35
Held to maturity, fair value less than 12 months	452	537
Held-to-maturity, gross, less than 12 months	3	4
Held to maturity, fair value 12 months or longer	190	204
Held to maturity, gross unrealized losses 12 months or longer	7	7
Held to maturity, fair value total	642	741
Held to maturity, gross unrealized losses total	10	11
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	888	944
Available for sale, gross unrealized losses less than 12 months	19	24
Available for sale, fair value 12 months or longer	158	157
Available for sale, gross unrealized losses 12 months or longer	6	6
Available for sale, fair value total	1,046	1,101
Available for sale, gross unrealized losses total	25	30
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	8
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	6	5
Available for sale, gross unrealized losses 12 months or longer	2	3
Available for sale, fair value total	6	13
Available for sale, gross unrealized losses total	$ 2	$ 3