Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 15,494	$ 16,928
Available for sale, gross unrealized losses less than 12 months	185	308
Available for sale, fair value 12 months or longer	5,071	7,800
Available for sale, gross unrealized losses 12 months or longer	75	177
Available for sale, fair value total	20,565	24,728
Available for sale, gross unrealized losses total	260	485
Held to maturity, fair value less than 12 months	16,982	17,284
Held-to-maturity, gross, less than 12 months	244	293
Held to maturity, fair value 12 months or longer	1,279	1,899
Held to maturity, gross unrealized losses 12 months or longer	23	42
Held to maturity, fair value total	18,261	19,183
Held to maturity, gross unrealized losses total	267	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	154	651
Available for sale, gross unrealized losses less than 12 months	1	8
Available for sale, fair value 12 months or longer	164	180
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	318	831
Available for sale, gross unrealized losses total	2	9
Held to maturity, fair value less than 12 months	9,025	8,891
Held-to-maturity, gross, less than 12 months	34	57
Held to maturity, fair value 12 months or longer	79	86
Held to maturity, gross unrealized losses 12 months or longer	1	1
Held to maturity, fair value total	9,104	8,977
Held to maturity, gross unrealized losses total	35	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	5,877	7,072
Available for sale, gross unrealized losses less than 12 months	83	131
Available for sale, fair value 12 months or longer	536	1,114
Available for sale, gross unrealized losses 12 months or longer	9	28
Available for sale, fair value total	6,413	8,186
Available for sale, gross unrealized losses total	92	159
Held to maturity, fair value less than 12 months	6,901	6,838
Held-to-maturity, gross, less than 12 months	200	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	6,901	6,838
Held to maturity, gross unrealized losses total	200	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	233	54
Available for sale, gross unrealized losses less than 12 months	1	0
Available for sale, fair value 12 months or longer	2,449	3,745
Available for sale, gross unrealized losses 12 months or longer	19	75
Available for sale, fair value total	2,682	3,799
Available for sale, gross unrealized losses total	20	75
Held to maturity, fair value less than 12 months	619	705
Held-to-maturity, gross, less than 12 months	8	9
Held to maturity, fair value 12 months or longer	728	1,235
Held to maturity, gross unrealized losses 12 months or longer	7	21
Held to maturity, fair value total	1,347	1,940
Held to maturity, gross unrealized losses total	15	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	498	494
Available for sale, gross unrealized losses 12 months or longer	22	25
Available for sale, fair value total	498	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	216	252
Available for sale, gross unrealized losses 12 months or longer	8	18
Available for sale, fair value total	216	253
Available for sale, gross unrealized losses total	8	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	233	925
Available for sale, gross unrealized losses less than 12 months	1	1
Available for sale, fair value 12 months or longer	3,163	4,491
Available for sale, gross unrealized losses 12 months or longer	49	118
Available for sale, fair value total	3,396	5,416
Available for sale, gross unrealized losses total	50	119
Held to maturity, fair value less than 12 months	619	756
Held-to-maturity, gross, less than 12 months	8	9
Held to maturity, fair value 12 months or longer	728	1,244
Held to maturity, gross unrealized losses 12 months or longer	7	21
Held to maturity, fair value total	1,347	2,000
Held to maturity, gross unrealized losses total	15	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	342	442
Available for sale, gross unrealized losses less than 12 months	1	1
Available for sale, fair value 12 months or longer	648	893
Available for sale, gross unrealized losses 12 months or longer	2	5
Available for sale, fair value total	990	1,335
Available for sale, gross unrealized losses total	3	6
Held to maturity, fair value less than 12 months	0	54
Held-to-maturity, gross, less than 12 months	0	2
Held to maturity, fair value 12 months or longer	290	330
Held to maturity, gross unrealized losses 12 months or longer	10	13
Held to maturity, fair value total	290	384
Held to maturity, gross unrealized losses total	10	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		253
Available for sale, gross unrealized losses less than 12 months		0
Available for sale, fair value 12 months or longer		276
Available for sale, gross unrealized losses 12 months or longer		1
Available for sale, fair value total		529
Available for sale, gross unrealized losses total		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	4,471	1,314
Available for sale, gross unrealized losses less than 12 months	20	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	4,471	1,314
Available for sale, gross unrealized losses total	20	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	728	670
Available for sale, gross unrealized losses less than 12 months	5	4
Available for sale, fair value 12 months or longer	0	218
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	728	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	5,541	2,679
Available for sale, gross unrealized losses less than 12 months	26	11
Available for sale, fair value 12 months or longer	648	1,387
Available for sale, gross unrealized losses 12 months or longer	2	7
Available for sale, fair value total	6,189	4,066
Available for sale, gross unrealized losses total	28	18
Held to maturity, fair value less than 12 months	0	262
Held-to-maturity, gross, less than 12 months	0	2
Held to maturity, fair value 12 months or longer	290	365
Held to maturity, gross unrealized losses 12 months or longer	10	13
Held to maturity, fair value total	290	627
Held to maturity, gross unrealized losses total	10	15
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,636	3,390
Available for sale, gross unrealized losses less than 12 months	33	102
Available for sale, fair value 12 months or longer	224	304
Available for sale, gross unrealized losses 12 months or longer	4	10
Available for sale, fair value total	1,860	3,694
Available for sale, gross unrealized losses total	37	112
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	906	1,259
Available for sale, gross unrealized losses less than 12 months	23	31
Available for sale, fair value 12 months or longer	171	162
Available for sale, gross unrealized losses 12 months or longer	4	4
Available for sale, fair value total	1,077	1,421
Available for sale, gross unrealized losses total	27	35
Held to maturity, fair value less than 12 months	437	537
Held-to-maturity, gross, less than 12 months	2	4
Held to maturity, fair value 12 months or longer	182	204
Held to maturity, gross unrealized losses 12 months or longer	5	7
Held to maturity, fair value total	619	741
Held to maturity, gross unrealized losses total	7	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	1,147	944
Available for sale, gross unrealized losses less than 12 months	18	24
Available for sale, fair value 12 months or longer	159	157
Available for sale, gross unrealized losses 12 months or longer	4	6
Available for sale, fair value total	1,306	1,101
Available for sale, gross unrealized losses total	22	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