Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Credit Derivatives [Line Items]
Notional Amount	$ 1,046	$ 1,269	$ 1,239
Single Name Credit Default Swaps
Credit Derivatives [Line Items]
Notional Amount	553	903	878
Average Term (Years)	2 years 3 months 7 days	2 years 3 months 7 days	2 years 1 month 8 days
Payment / Performance Risk	3.74%	3.89%	4.98%
Traded Credit Default Swap Indices
Credit Derivatives [Line Items]
Notional Amount	466	346	343
Average Term (Years)	2 years 6 months 6 days	3 years 4 months 5 days	3 years 2 months
Payment / Performance Risk	3.56%	4.04%	4.58%
Other
Credit Derivatives [Line Items]
Notional Amount	$ 27	$ 20	$ 18
Average Term (Years)	5 years 3 months 2 days	5 years 5 months 5 days	5 years 7 months 4 days
Payment / Performance Risk	11.53%	10.82%	10.89%