Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Credit Derivatives [Line Items]
Notional Amount	$ 83	$ 913	$ 169
Average Term (Years)	0 years	0 years	0 years
Payment / Performance Risk
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Notional Amount	67	420	146
Average Term (Years)	10 months 28 days	2 years	11 months 1 day
Payment / Performance Risk	21.26%	4.32%	11.62%
Traded Credit Default Swap Indices [Member]
Credit Derivatives [Line Items]
Notional Amount		466
Average Term (Years)		2 years 7 months 28 days
Payment / Performance Risk		3.56%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 16	$ 27	$ 23
Average Term (Years)	5 years 1 month 10 days	5 years 3 months 26 days	5 years 4 months 6 days
Payment / Performance Risk	8.72%	11.53%	10.77%