Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	$ 13,338	$ 8,532
Available for sale, Gross Unrealized Losses Less than 12 months	106	39
Available for sale, Fair Value 12 months or longer	11,349	16,983
Available for sale, Gross Unrealized Losses 12 months or longer	293	385
Available for sale, Fair Value Total	24,687	25,515
Available for sale, Gross Unrealized Losses Total	399	424
Held to maturity, Fair Value Less than 12 months	3,492	2,608
Held-to-maturity, Gross, Less than 12 Months	59	13
Held to maturity, Fair Value 12 months or longer	4,233	6,220
Held to maturity, Gross Unrealized Losses 12 months or longer	142	177
Held to maturity, Fair Value Total	7,725	8,828
Held to maturity, Gross Unrealized Losses Total	201	190
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	2,074	2,364
Available for sale, Gross Unrealized Losses Less than 12 months	13	17
Available for sale, Fair Value 12 months or longer	5,403	7,982
Available for sale, Gross Unrealized Losses 12 months or longer	144	207
Available for sale, Fair Value Total	7,477	10,346
Available for sale, Gross Unrealized Losses Total	157	224
Held to maturity, Fair Value Less than 12 months	671	904
Held-to-maturity, Gross, Less than 12 Months	3	4
Held to maturity, Fair Value 12 months or longer	243	192
Held to maturity, Gross Unrealized Losses 12 months or longer	1	1
Held to maturity, Fair Value Total	914	1,096
Held to maturity, Gross Unrealized Losses Total	4	5
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	405	0
Available for sale, Gross Unrealized Losses Less than 12 months	1	0
Available for sale, Fair Value 12 months or longer	112	167
Available for sale, Gross Unrealized Losses 12 months or longer	1	1
Available for sale, Fair Value Total	517	167
Available for sale, Gross Unrealized Losses Total	2	1
Held to maturity, Fair Value Less than 12 months	1,952	76
Held-to-maturity, Gross, Less than 12 Months	50	1
Held to maturity, Fair Value 12 months or longer	2,993	4,891
Held to maturity, Gross Unrealized Losses 12 months or longer	112	146
Held to maturity, Fair Value Total	4,945	4,967
Held to maturity, Gross Unrealized Losses Total	162	147
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	5,106	2,569
Available for sale, Gross Unrealized Losses Less than 12 months	37	9
Available for sale, Fair Value 12 months or longer	4,128	6,466
Available for sale, Gross Unrealized Losses 12 months or longer	92	118
Available for sale, Fair Value Total	9,234	9,035
Available for sale, Gross Unrealized Losses Total	129	127
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	1,693	1,473
Available for sale, Gross Unrealized Losses Less than 12 months	12	15
Available for sale, Fair Value 12 months or longer	3,319	5,025
Available for sale, Gross Unrealized Losses 12 months or longer	81	109
Available for sale, Fair Value Total	5,012	6,498
Available for sale, Gross Unrealized Losses Total	93	124
Held to maturity, Fair Value Less than 12 months	671	780
Held-to-maturity, Gross, Less than 12 Months	3	3
Held to maturity, Fair Value 12 months or longer	243	192
Held to maturity, Gross Unrealized Losses 12 months or longer	1	1
Held to maturity, Fair Value Total	914	972
Held to maturity, Gross Unrealized Losses Total	4	4
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	60	344
Available for sale, Gross Unrealized Losses Less than 12 months	0	1
Available for sale, Fair Value 12 months or longer	1,281	1,270
Available for sale, Gross Unrealized Losses 12 months or longer	30	33
Available for sale, Fair Value Total	1,341	1,614
Available for sale, Gross Unrealized Losses Total	30	34
Held to maturity, Fair Value Less than 12 months		124
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		124
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	11	0
Available for sale, Gross Unrealized Losses Less than 12 months	0	0
Available for sale, Fair Value 12 months or longer	446	896
Available for sale, Gross Unrealized Losses 12 months or longer	31	56
Available for sale, Fair Value Total	457	896
Available for sale, Gross Unrealized Losses Total	31	56
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	310	547
Available for sale, Gross Unrealized Losses Less than 12 months	1	1
Available for sale, Fair Value 12 months or longer	357	791
Available for sale, Gross Unrealized Losses 12 months or longer	2	9
Available for sale, Fair Value Total	667	1,338
Available for sale, Gross Unrealized Losses Total	3	10
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	1,827	1,931
Available for sale, Gross Unrealized Losses Less than 12 months	8	6
Available for sale, Fair Value 12 months or longer	621	498
Available for sale, Gross Unrealized Losses 12 months or longer	3	5
Available for sale, Fair Value Total	2,448	2,429
Available for sale, Gross Unrealized Losses Total	11	11
Held to maturity, Fair Value Less than 12 months	466	1,206
Held-to-maturity, Gross, Less than 12 Months	2	4
Held to maturity, Fair Value 12 months or longer	576	590
Held to maturity, Gross Unrealized Losses 12 months or longer	21	19
Held to maturity, Fair Value Total	1,042	1,796
Held to maturity, Gross Unrealized Losses Total	23	23
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	909	1,350
Available for sale, Gross Unrealized Losses Less than 12 months	4	2
Available for sale, Fair Value 12 months or longer	210	170
Available for sale, Gross Unrealized Losses 12 months or longer	2	2
Available for sale, Fair Value Total	1,119	1,520
Available for sale, Gross Unrealized Losses Total	6	4
Held to maturity, Fair Value Less than 12 months	466	507
Held-to-maturity, Gross, Less than 12 Months	2	3
Held to maturity, Fair Value 12 months or longer	532	590
Held to maturity, Gross Unrealized Losses 12 months or longer	20	19
Held to maturity, Fair Value Total	998	1,097
Held to maturity, Gross Unrealized Losses Total	22	22
Non-U.S. debt securities, asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, Fair Value Less than 12 months		699
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		699
Held to maturity, Gross Unrealized Losses Total		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	918	581
Available for sale, Gross Unrealized Losses Less than 12 months	4	4
Available for sale, Fair Value 12 months or longer	411	328
Available for sale, Gross Unrealized Losses 12 months or longer	1	3
Available for sale, Fair Value Total	1,329	909
Available for sale, Gross Unrealized Losses Total	5	7
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	44
Held to maturity, Gross Unrealized Losses 12 months or longer	1
Held to maturity, Fair Value Total	44
Held to maturity, Gross Unrealized Losses Total	1
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	2,319	610
Available for sale, Gross Unrealized Losses Less than 12 months	34	3
Available for sale, Fair Value 12 months or longer	779	1,315
Available for sale, Gross Unrealized Losses 12 months or longer	40	34
Available for sale, Fair Value Total	3,098	1,925
Available for sale, Gross Unrealized Losses Total	74	37
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	1,297	731
Available for sale, Gross Unrealized Losses Less than 12 months	9	2
Available for sale, Fair Value 12 months or longer	161	311
Available for sale, Gross Unrealized Losses 12 months or longer	5	10
Available for sale, Fair Value Total	1,458	1,042
Available for sale, Gross Unrealized Losses Total	14	12
Held to maturity, Fair Value Less than 12 months	403	422
Held-to-maturity, Gross, Less than 12 Months	4	4
Held to maturity, Fair Value 12 months or longer	421	547
Held to maturity, Gross Unrealized Losses 12 months or longer	8	11
Held to maturity, Fair Value Total	824	969
Held to maturity, Gross Unrealized Losses Total	12	15
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	304	327
Available for sale, Gross Unrealized Losses Less than 12 months	3	2
Available for sale, Fair Value 12 months or longer	145	244
Available for sale, Gross Unrealized Losses 12 months or longer	8	10
Available for sale, Fair Value Total	449	571
Available for sale, Gross Unrealized Losses Total	11	$ 12
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	6
Available for sale, Gross Unrealized Losses Less than 12 months	1
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	6
Available for sale, Gross Unrealized Losses Total	$ 1