Investment Securities (Schedule of Contractual Maturities of Debt Securities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	$ 9,647
Available for sale, 1 to 5 Years	37,558
Available for sale, 6 to 10 Years	21,022
Available for sale, Over 10 Years	30,860
Held to maturity, Under 1 Year	427
Held to maturity, 1 to 5 Years	4,302
Held to maturity, 6 to 10 Years	6,679
Held to maturity, Over 10 Years	5,290
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	4,305
Available for sale, 1 to 5 Years	11,805
Available for sale, 6 to 10 Years	8,281
Available for sale, Over 10 Years	5,273
Held to maturity, Under 1 Year	19
Held to maturity, 1 to 5 Years	892
Held to maturity, 6 to 10 Years	823
Held to maturity, Over 10 Years	1,117
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	0
Available for sale, 1 to 5 Years	42
Available for sale, 6 to 10 Years	46
Available for sale, Over 10 Years	650
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	3
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	103
Available for sale, 1 to 5 Years	1,847
Available for sale, 6 to 10 Years	6,188
Available for sale, Over 10 Years	16,437
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	25
Held to maturity, 6 to 10 Years	19
Held to maturity, Over 10 Years	56
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	1,019
Available for sale, 1 to 5 Years	6,513
Available for sale, 6 to 10 Years	4,646
Available for sale, Over 10 Years	2,693
Held to maturity, Under 1 Year	19
Held to maturity, 1 to 5 Years	153
Held to maturity, 6 to 10 Years	219
Held to maturity, Over 10 Years	1,111
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,919
Available for sale, 1 to 5 Years	3,506
Available for sale, 6 to 10 Years	2,201
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	229
Held to maturity, 6 to 10 Years	302
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	26
Available for sale, 1 to 5 Years	28
Available for sale, 6 to 10 Years	2
Available for sale, Over 10 Years	1,210
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	341
Available for sale, 1 to 5 Years	1,758
Available for sale, 6 to 10 Years	1,432
Available for sale, Over 10 Years	1,370
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	510
Held to maturity, 6 to 10 Years	302
Held to maturity, Over 10 Years	6
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	4,085
Available for sale, 1 to 5 Years	14,788
Available for sale, 6 to 10 Years	1,082
Available for sale, Over 10 Years	4,654
Held to maturity, Under 1 Year	258
Held to maturity, 1 to 5 Years	2,198
Held to maturity, 6 to 10 Years	335
Held to maturity, Over 10 Years	3,010
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	148
Available for sale, 1 to 5 Years	6,191
Available for sale, 6 to 10 Years	159
Available for sale, Over 10 Years	4,503
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	939
Held to maturity, 6 to 10 Years	164
Held to maturity, Over 10 Years	3,006
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	253
Available for sale, 1 to 5 Years	4,685
Available for sale, 6 to 10 Years	378
Available for sale, Over 10 Years	151
Held to maturity, Under 1 Year	80
Held to maturity, 1 to 5 Years	1,235
Held to maturity, 6 to 10 Years	171
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	2,541
Available for sale, 1 to 5 Years	1,000
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	16
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	1,143
Available for sale, 1 to 5 Years	2,912
Available for sale, 6 to 10 Years	545
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	162
Held to maturity, 1 to 5 Years	24
Held to maturity, 6 to 10 Years	0
Held to maturity, Over 10 Years	4
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	668
Available for sale, 1 to 5 Years	3,059
Available for sale, 6 to 10 Years	3,565
Available for sale, Over 10 Years	2,006
Held to maturity, Under 1 Year	48
Held to maturity, 1 to 5 Years	13
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	271
Available for sale, 1 to 5 Years	1,923
Available for sale, 6 to 10 Years	1,157
Available for sale, Over 10 Years	1,807
Held to maturity, Under 1 Year	102
Held to maturity, 1 to 5 Years	1,174
Held to maturity, 6 to 10 Years	502
Held to maturity, Over 10 Years	1,104
Other U.S.debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	215
Available for sale, 1 to 5 Years	4,094
Available for sale, 6 to 10 Years	703
Available for sale, Over 10 Years	$ 33