Guarantee Arrangements and Pledged Assets - Carrying Value and Contractual Amounts of our Sell Protection Credit Derivatives and Major Off-Balance Sheet Guarantee Arrangements (Parenthetical) (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Guarantor Obligations [Line Items]
Net contingent liabilities	$ 0
Credit derivatives [Member]
Guarantor Obligations [Line Items]
Guarantee Arrangement for the benefit of Affiliates	45,900,000,000	45,100,000,000
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Guarantee Arrangement for the benefit of Affiliates	$ 757,000,000,000	$ 707,000,000,000