Investment Securities (Schedule of Contractual Maturities of Debt Securities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	$ 9,460
Available for sale, 1 to 5 Years	37,394
Available for sale, 6 to 10 Years	21,706
Available for sale, Over 10 Years	27,410
Held to maturity, Under 1 Year	1,050
Held to maturity, 1 to 5 Years	5,860
Held to maturity, 6 to 10 Years	7,150
Held to maturity, Over 10 Years	4,707
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	913
Available for sale, 1 to 5 Years	9,168
Available for sale, 6 to 10 Years	6,190
Available for sale, Over 10 Years	4,986
Held to maturity, Under 1 Year	26
Held to maturity, 1 to 5 Years	958
Held to maturity, 6 to 10 Years	1,123
Held to maturity, Over 10 Years	1,296
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	151
Available for sale, 1 to 5 Years	6,766
Available for sale, 6 to 10 Years	3,300
Available for sale, Over 10 Years	547
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	117
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	2,441
Available for sale, 6 to 10 Years	4,753
Available for sale, Over 10 Years	13,824
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	15
Held to maturity, 6 to 10 Years	13
Held to maturity, Over 10 Years	40
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	342
Available for sale, 1 to 5 Years	6,572
Available for sale, 6 to 10 Years	3,750
Available for sale, Over 10 Years	2,142
Held to maturity, Under 1 Year	7
Held to maturity, 1 to 5 Years	182
Held to maturity, 6 to 10 Years	393
Held to maturity, Over 10 Years	1,291
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	307
Available for sale, 1 to 5 Years	1,513
Available for sale, 6 to 10 Years	1,291
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	9
Available for sale, 1 to 5 Years	14
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	974
Asset-backed securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	255
Available for sale, 1 to 5 Years	1,069
Available for sale, 6 to 10 Years	1,149
Available for sale, Over 10 Years	1,870
Held to maturity, Under 1 Year	19
Held to maturity, 1 to 5 Years	401
Held to maturity, 6 to 10 Years	208
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	6,496
Available for sale, 1 to 5 Years	11,612
Available for sale, 6 to 10 Years	1,612
Available for sale, Over 10 Years	3,428
Held to maturity, Under 1 Year	438
Held to maturity, 1 to 5 Years	4,334
Held to maturity, 6 to 10 Years	511
Held to maturity, Over 10 Years	2,348
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	2,190
Available for sale, 1 to 5 Years	4,344
Available for sale, 6 to 10 Years	384
Available for sale, Over 10 Years	3,321
Held to maturity, Under 1 Year	323
Held to maturity, 1 to 5 Years	1,208
Held to maturity, 6 to 10 Years	274
Held to maturity, Over 10 Years	2,348
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	359
Available for sale, 1 to 5 Years	2,691
Available for sale, 6 to 10 Years	290
Available for sale, Over 10 Years	107
Held to maturity, Under 1 Year	5
Held to maturity, 1 to 5 Years	3,051
Held to maturity, 6 to 10 Years	237
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	1,978
Available for sale, 1 to 5 Years	1,635
Available for sale, 6 to 10 Years	0
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	110
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	1,969
Available for sale, 1 to 5 Years	2,942
Available for sale, 6 to 10 Years	938
Available for sale, Over 10 Years	0
Held to maturity, Under 1 Year	0
Held to maturity, 1 to 5 Years	75
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	731
Available for sale, 1 to 5 Years	3,021
Available for sale, 6 to 10 Years	4,451
Available for sale, Over 10 Years	2,442
Held to maturity, Under 1 Year	9
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	286
Available for sale, 1 to 5 Years	1,165
Available for sale, 6 to 10 Years	1,072
Available for sale, Over 10 Years	2,148
Held to maturity, Under 1 Year	577
Held to maturity, 1 to 5 Years	550
Held to maturity, 6 to 10 Years	503
Held to maturity, Over 10 Years	906
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, Under 1 Year	700
Available for sale, 1 to 5 Years	3,221
Available for sale, 6 to 10 Years	328
Available for sale, Over 10 Years	$ 35