Investment Securities (Schedule of Contractual Maturities of Debt Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	$ 11,305
Available for sale, 1 to 5 Years	35,501
Available for sale, 6 to 10 Years	21,072
Available for sale, Over 10 Years	30,247
Held to maturity, Under 1 Year	554
Held to maturity, 1 to 5 Years	5,257
Held to maturity, 6 to 10 Years	7,158
Held to maturity, Over 10 Years	5,373
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	3,310
Available for sale, 1 to 5 Years	10,999
Available for sale, 6 to 10 Years	7,591
Available for sale, Over 10 Years	5,652
Held to maturity, Under 1 Year	42
Held to maturity, 1 to 5 Years	974
Held to maturity, 6 to 10 Years	1,208
Held to maturity, Over 10 Years	1,300
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	526
Available for sale, 6 to 10 Years	835
Available for sale, Over 10 Years	600
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	5,000
Held to maturity, Over 10 Years	96
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	183
Available for sale, 1 to 5 Years	2,387
Available for sale, 6 to 10 Years	5,276
Available for sale, Over 10 Years	15,246
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	19
Held to maturity, 6 to 10 Years	16
Held to maturity, Over 10 Years	46
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	647
Available for sale, 1 to 5 Years	6,608
Available for sale, 6 to 10 Years	4,216
Available for sale, Over 10 Years	2,809
Held to maturity, Under 1 Year	19
Held to maturity, 1 to 5 Years	192
Held to maturity, 6 to 10 Years	383
Held to maturity, Over 10 Years	1,295
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,187
Available for sale, 1 to 5 Years	3,057
Available for sale, 6 to 10 Years	1,993
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	335
Held to maturity, 6 to 10 Years	562
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	7
Available for sale, 1 to 5 Years	20
Available for sale, 6 to 10 Years	1
Available for sale, Over 10 Years	1,127
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	469
Available for sale, 1 to 5 Years	1,314
Available for sale, 6 to 10 Years	1,381
Available for sale, Over 10 Years	1,716
Held to maturity, Under 1 Year	23
Held to maturity, 1 to 5 Years	447
Held to maturity, 6 to 10 Years	263
Held to maturity, Over 10 Years	5
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	6,248
Available for sale, 1 to 5 Years	13,248
Available for sale, 6 to 10 Years	1,547
Available for sale, Over 10 Years	3,823
Held to maturity, Under 1 Year	261
Held to maturity, 1 to 5 Years	3,301
Held to maturity, 6 to 10 Years	438
Held to maturity, Over 10 Years	2,916
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,698
Available for sale, 1 to 5 Years	5,562
Available for sale, 6 to 10 Years	247
Available for sale, Over 10 Years	3,689
Held to maturity, Under 1 Year	23
Held to maturity, 1 to 5 Years	1,191
Held to maturity, 6 to 10 Years	194
Held to maturity, Over 10 Years	2,915
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	3,906
Available for sale, 6 to 10 Years	599
Available for sale, Over 10 Years	134
Held to maturity, Under 1 Year	70
Held to maturity, 1 to 5 Years	2,085
Held to maturity, 6 to 10 Years	244
Held to maturity, Over 10 Years	0
Non-US debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,537
Available for sale, 1 to 5 Years	1,155
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	2
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	1,658
Available for sale, 1 to 5 Years	2,625
Available for sale, 6 to 10 Years	701
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	166
Held to maturity, 1 to 5 Years	25
Held to maturity, 6 to 10 Years	0
Held to maturity, Over 10 Years	1
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	672
Available for sale, 1 to 5 Years	3,122
Available for sale, 6 to 10 Years	4,049
Available for sale, Over 10 Years	2,601
Held to maturity, Under 1 Year	13
Held to maturity, 1 to 5 Years	3
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	453
Available for sale, 1 to 5 Years	1,458
Available for sale, 6 to 10 Years	1,059
Available for sale, Over 10 Years	2,292
Held to maturity, Under 1 Year	238
Held to maturity, 1 to 5 Years	960
Held to maturity, 6 to 10 Years	496
Held to maturity, Over 10 Years	1,015
Other U.S.debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	437
Available for sale, 1 to 5 Years	3,761
Available for sale, 6 to 10 Years	715
Available for sale, Over 10 Years	$ 33