Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Jun. 30, 2015 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	$ 8,965
Available for sale, 1 to 5 Years	31,709
Available for sale, 6 to 10 Years	19,380
Available for sale, Over 10 Years	24,919
Held to maturity, Under 1 Year	1,232
Held to maturity, 1 to 5 Years	4,240
Held to maturity, 6 to 10 Years	6,901
Held to maturity, Over 10 Years	3,782
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	678
Available for sale, 1 to 5 Years	4,955
Available for sale, 6 to 10 Years	5,235
Available for sale, Over 10 Years	3,333
Held to maturity, Under 1 Year	60
Held to maturity, 1 to 5 Years	858
Held to maturity, 6 to 10 Years	998
Held to maturity, Over 10 Years	1,178
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2
Available for sale, 1 to 5 Years	9,322
Available for sale, 6 to 10 Years	3,087
Available for sale, Over 10 Years	493
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	492
Held to maturity, 6 to 10 Years	5,104
Held to maturity, Over 10 Years	111
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	88
Available for sale, 1 to 5 Years	2,273
Available for sale, 6 to 10 Years	3,812
Available for sale, Over 10 Years	13,545
Held to maturity, Under 1 Year	3
Held to maturity, 1 to 5 Years	5
Held to maturity, 6 to 10 Years	10
Held to maturity, Over 10 Years	33
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	448
Available for sale, 1 to 5 Years	4,091
Available for sale, 6 to 10 Years	3,248
Available for sale, Over 10 Years	1,351
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	194
Held to maturity, 6 to 10 Years	328
Held to maturity, Over 10 Years	1,174
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	176
Available for sale, 1 to 5 Years	310
Available for sale, 6 to 10 Years	1,083
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	375
Held to maturity, 6 to 10 Years	522
Held to maturity, Over 10 Years	0
Asset-backed securities, sub-prime
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	8
Available for sale, 1 to 5 Years	6
Available for sale, 6 to 10 Years	4
Available for sale, Over 10 Years	472
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	46
Available for sale, 1 to 5 Years	548
Available for sale, 6 to 10 Years	900
Available for sale, Over 10 Years	1,510
Held to maturity, Under 1 Year	60
Held to maturity, 1 to 5 Years	289
Held to maturity, 6 to 10 Years	148
Held to maturity, Over 10 Years	4
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	6,344
Available for sale, 1 to 5 Years	9,846
Available for sale, 6 to 10 Years	1,434
Available for sale, Over 10 Years	2,758
Held to maturity, Under 1 Year	757
Held to maturity, 1 to 5 Years	2,697
Held to maturity, 6 to 10 Years	293
Held to maturity, Over 10 Years	1,656
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,778
Available for sale, 1 to 5 Years	3,194
Available for sale, 6 to 10 Years	625
Available for sale, Over 10 Years	2,732
Held to maturity, Under 1 Year	474
Held to maturity, 1 to 5 Years	869
Held to maturity, 6 to 10 Years	121
Held to maturity, Over 10 Years	1,656
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	355
Available for sale, 1 to 5 Years	2,481
Available for sale, 6 to 10 Years	70
Available for sale, Over 10 Years	26
Held to maturity, Under 1 Year	106
Held to maturity, 1 to 5 Years	1,783
Held to maturity, 6 to 10 Years	172
Held to maturity, Over 10 Years	0
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,941
Available for sale, 1 to 5 Years	1,049
Available for sale, 6 to 10 Years	13
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	153
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, Over 10 Years	0
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,270
Available for sale, 1 to 5 Years	3,122
Available for sale, 6 to 10 Years	726
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	24
Held to maturity, 1 to 5 Years	45
Held to maturity, 6 to 10 Years	0
Held to maturity, Over 10 Years	0
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	684
Available for sale, 1 to 5 Years	2,600
Available for sale, 6 to 10 Years	4,926
Available for sale, Over 10 Years	2,239
Held to maturity, Under 1 Year	3
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, Over 10 Years	0
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	262
Available for sale, 1 to 5 Years	546
Available for sale, 6 to 10 Years	660
Available for sale, Over 10 Years	2,516
Held to maturity, Under 1 Year	409
Held to maturity, 1 to 5 Years	188
Held to maturity, 6 to 10 Years	496
Held to maturity, Over 10 Years	804
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	907
Available for sale, 1 to 5 Years	2,167
Available for sale, 6 to 10 Years	226
Available for sale, Over 10 Years	$ 35