Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	$ 11,782	$ 8,532
Available for sale, Gross Unrealized Losses Less than 12 months	111	39
Available for sale, Fair Value 12 months or longer	9,104	16,983
Available for sale, Gross Unrealized Losses 12 months or longer	298	385
Available for sale, Fair Value Total	20,886	25,515
Available for sale, Gross Unrealized Losses Total	409	424
Held to maturity, Fair Value Less than 12 months	5,401	2,608
Held-to-maturity, Gross, Less than 12 Months	52	13
Held to maturity, Fair Value 12 months or longer	4,494	6,220
Held to maturity, Gross Unrealized Losses 12 months or longer	110	177
Held to maturity, Fair Value Total	9,895	8,828
Held to maturity, Gross Unrealized Losses Total	162	190
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	3,372	2,364
Available for sale, Gross Unrealized Losses Less than 12 months	64	17
Available for sale, Fair Value 12 months or longer	3,770	7,982
Available for sale, Gross Unrealized Losses 12 months or longer	185	207
Available for sale, Fair Value Total	7,142	10,346
Available for sale, Gross Unrealized Losses Total	249	224
Held to maturity, Fair Value Less than 12 months	1,204	904
Held-to-maturity, Gross, Less than 12 Months	27	4
Held to maturity, Fair Value 12 months or longer	419	192
Held to maturity, Gross Unrealized Losses 12 months or longer	10	1
Held to maturity, Fair Value Total	1,623	1,096
Held to maturity, Gross Unrealized Losses Total	37	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	0	0
Available for sale, Gross Unrealized Losses Less than 12 months	0	0
Available for sale, Fair Value 12 months or longer	125	167
Available for sale, Gross Unrealized Losses 12 months or longer	1	1
Available for sale, Fair Value Total	125	167
Available for sale, Gross Unrealized Losses Total	1	1
Held to maturity, Fair Value Less than 12 months	1,990	76
Held-to-maturity, Gross, Less than 12 Months	14	1
Held to maturity, Fair Value 12 months or longer	3,048	4,891
Held to maturity, Gross Unrealized Losses 12 months or longer	57	146
Held to maturity, Fair Value Total	5,038	4,967
Held to maturity, Gross Unrealized Losses Total	71	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	1,411	2,569
Available for sale, Gross Unrealized Losses Less than 12 months	9	9
Available for sale, Fair Value 12 months or longer	3,331	6,466
Available for sale, Gross Unrealized Losses 12 months or longer	52	118
Available for sale, Fair Value Total	4,742	9,035
Available for sale, Gross Unrealized Losses Total	61	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	3,372	1,473
Available for sale, Gross Unrealized Losses Less than 12 months	64	15
Available for sale, Fair Value 12 months or longer	2,762	5,025
Available for sale, Gross Unrealized Losses 12 months or longer	128	109
Available for sale, Fair Value Total	6,134	6,498
Available for sale, Gross Unrealized Losses Total	192	124
Held to maturity, Fair Value Less than 12 months	1,204	780
Held-to-maturity, Gross, Less than 12 Months	27	3
Held to maturity, Fair Value 12 months or longer	385	192
Held to maturity, Gross Unrealized Losses 12 months or longer	9	1
Held to maturity, Fair Value Total	1,589	972
Held to maturity, Gross Unrealized Losses Total	36	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	0	344
Available for sale, Gross Unrealized Losses Less than 12 months	0	1
Available for sale, Fair Value 12 months or longer	498	1,270
Available for sale, Gross Unrealized Losses 12 months or longer	27	33
Available for sale, Fair Value Total	498	1,614
Available for sale, Gross Unrealized Losses Total	27	34
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	0
Available for sale, Gross Unrealized Losses Less than 12 months	0	0
Available for sale, Fair Value 12 months or longer	419	896
Available for sale, Gross Unrealized Losses 12 months or longer	29	56
Available for sale, Fair Value Total	419	896
Available for sale, Gross Unrealized Losses Total	29	56
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	0	547
Available for sale, Gross Unrealized Losses Less than 12 months	0	1
Available for sale, Fair Value 12 months or longer	91	791
Available for sale, Gross Unrealized Losses 12 months or longer	1	9
Available for sale, Fair Value Total	91	1,338
Available for sale, Gross Unrealized Losses Total	1	10
Held to maturity, Fair Value Less than 12 months	0	124
Held-to-maturity, Gross, Less than 12 Months	0	1
Held to maturity, Fair Value 12 months or longer	34	0
Held to maturity, Gross Unrealized Losses 12 months or longer	1	0
Held to maturity, Fair Value Total	34	124
Held to maturity, Gross Unrealized Losses Total	1	1
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	5,254	1,931
Available for sale, Gross Unrealized Losses Less than 12 months	21	6
Available for sale, Fair Value 12 months or longer	711	498
Available for sale, Gross Unrealized Losses 12 months or longer	6	5
Available for sale, Fair Value Total	5,965	2,429
Available for sale, Gross Unrealized Losses Total	27	11
Held to maturity, Fair Value Less than 12 months	1,755	1,206
Held-to-maturity, Gross, Less than 12 Months	6	4
Held to maturity, Fair Value 12 months or longer	480	590
Held to maturity, Gross Unrealized Losses 12 months or longer	28	19
Held to maturity, Fair Value Total	2,235	1,796
Held to maturity, Gross Unrealized Losses Total	34	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	2,030	1,350
Available for sale, Gross Unrealized Losses Less than 12 months	9	2
Available for sale, Fair Value 12 months or longer	197	170
Available for sale, Gross Unrealized Losses 12 months or longer	3	2
Available for sale, Fair Value Total	2,227	1,520
Available for sale, Gross Unrealized Losses Total	12	4
Held to maturity, Fair Value Less than 12 months	613	507
Held-to-maturity, Gross, Less than 12 Months	3	3
Held to maturity, Fair Value 12 months or longer	480	590
Held to maturity, Gross Unrealized Losses 12 months or longer	28	19
Held to maturity, Fair Value Total	1,093	1,097
Held to maturity, Gross Unrealized Losses Total	31	22
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	2,016
Available for sale, Gross Unrealized Losses Less than 12 months	5
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	2,016
Available for sale, Gross Unrealized Losses Total	5
Held to maturity, Fair Value Less than 12 months	1,142	699
Held-to-maturity, Gross, Less than 12 Months	3	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	1,142	699
Held to maturity, Gross Unrealized Losses Total	3	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	1,208	581
Available for sale, Gross Unrealized Losses Less than 12 months	7	4
Available for sale, Fair Value 12 months or longer	514	328
Available for sale, Gross Unrealized Losses 12 months or longer	3	3
Available for sale, Fair Value Total	1,722	909
Available for sale, Gross Unrealized Losses Total	10	7
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	818	610
Available for sale, Gross Unrealized Losses Less than 12 months	7	3
Available for sale, Fair Value 12 months or longer	824	1,315
Available for sale, Gross Unrealized Losses 12 months or longer	39	34
Available for sale, Fair Value Total	1,642	1,925
Available for sale, Gross Unrealized Losses Total	46	37
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	667	731
Available for sale, Gross Unrealized Losses Less than 12 months	5	2
Available for sale, Fair Value 12 months or longer	188	311
Available for sale, Gross Unrealized Losses 12 months or longer	6	10
Available for sale, Fair Value Total	855	1,042
Available for sale, Gross Unrealized Losses Total	11	12
Held to maturity, Fair Value Less than 12 months	452	422
Held-to-maturity, Gross, Less than 12 Months	5	4
Held to maturity, Fair Value 12 months or longer	547	547
Held to maturity, Gross Unrealized Losses 12 months or longer	15	11
Held to maturity, Fair Value Total	999	969
Held to maturity, Gross Unrealized Losses Total	20	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	255	327
Available for sale, Gross Unrealized Losses Less than 12 months	3	2
Available for sale, Fair Value 12 months or longer	155	244
Available for sale, Gross Unrealized Losses 12 months or longer	9	10
Available for sale, Fair Value Total	410	571
Available for sale, Gross Unrealized Losses Total	12	$ 12
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, Fair Value Less than 12 months	5
Available for sale, Gross Unrealized Losses Less than 12 months	2
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	5
Available for sale, Gross Unrealized Losses Total	$ 2