Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	$ 8,762
Available for sale, 1 to 5 Years	37,637
Available for sale, 6 to 10 Years	21,303
Available for sale, Over 10 Years	28,279
Held to maturity, Under 1 Year	1,255
Held to maturity, 1 to 5 Years	4,225
Held to maturity, 6 to 10 Years	6,853
Held to maturity, Over 10 Years	3,912
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	958
Available for sale, 1 to 5 Years	8,371
Available for sale, 6 to 10 Years	6,339
Available for sale, Over 10 Years	4,252
Held to maturity, Under 1 Year	13
Held to maturity, 1 to 5 Years	927
Held to maturity, 6 to 10 Years	1,041
Held to maturity, Over 10 Years	1,216
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1
Available for sale, 1 to 5 Years	9,246
Available for sale, 6 to 10 Years	3,238
Available for sale, Over 10 Years	511
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	4,999
Held to maturity, Over 10 Years	113
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	117
Available for sale, 1 to 5 Years	2,420
Available for sale, 6 to 10 Years	4,056
Available for sale, Over 10 Years	14,453
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	11
Held to maturity, 6 to 10 Years	11
Held to maturity, Over 10 Years	35
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	553
Available for sale, 1 to 5 Years	5,858
Available for sale, 6 to 10 Years	3,816
Available for sale, Over 10 Years	1,837
Held to maturity, Under 1 Year	4
Held to maturity, 1 to 5 Years	182
Held to maturity, 6 to 10 Years	357
Held to maturity, Over 10 Years	1,212
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	227
Available for sale, 1 to 5 Years	1,565
Available for sale, 6 to 10 Years	1,125
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	7
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	896
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	170
Available for sale, 1 to 5 Years	941
Available for sale, 6 to 10 Years	1,398
Available for sale, Over 10 Years	1,519
Held to maturity, Under 1 Year	9
Held to maturity, 1 to 5 Years	370
Held to maturity, 6 to 10 Years	162
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	5,627
Available for sale, 1 to 5 Years	11,034
Available for sale, 6 to 10 Years	1,364
Available for sale, Over 10 Years	3,042
Held to maturity, Under 1 Year	756
Held to maturity, 1 to 5 Years	2,997
Held to maturity, 6 to 10 Years	306
Held to maturity, Over 10 Years	1,727
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,661
Available for sale, 1 to 5 Years	3,511
Available for sale, 6 to 10 Years	513
Available for sale, Over 10 Years	2,979
Held to maturity, Under 1 Year	476
Held to maturity, 1 to 5 Years	939
Held to maturity, 6 to 10 Years	133
Held to maturity, Over 10 Years	1,727
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	390
Available for sale, 1 to 5 Years	2,796
Available for sale, 6 to 10 Years	112
Available for sale, Over 10 Years	63
Held to maturity, Under 1 Year	132
Held to maturity, 1 to 5 Years	1,993
Held to maturity, 6 to 10 Years	173
Held to maturity, Over 10 Years	0
Government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,236
Available for sale, 1 to 5 Years	1,575
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	148
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	1,340
Available for sale, 1 to 5 Years	3,152
Available for sale, 6 to 10 Years	739
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	65
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	723
Available for sale, 1 to 5 Years	2,848
Available for sale, 6 to 10 Years	4,952
Available for sale, Over 10 Years	2,526
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	249
Available for sale, 1 to 5 Years	1,044
Available for sale, 6 to 10 Years	1,077
Available for sale, Over 10 Years	3,460
Held to maturity, Under 1 Year	483
Held to maturity, 1 to 5 Years	290
Held to maturity, 6 to 10 Years	496
Held to maturity, Over 10 Years	821
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,087
Available for sale, 1 to 5 Years	2,674
Available for sale, 6 to 10 Years	277
Available for sale, Over 10 Years	$ 35

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of held-to-maturity debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of held-to-maturity debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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