Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Credit Derivatives [Line Items]
Notional Amount	$ 91	$ 1,051	$ 169
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Notional Amount	77	550	146
Average Term (Years)	1 year 18 days	2 years 5 months 1 day	11 months 1 day
Payment / Performance Risk	8.84%	4.40%	11.62%
Traded Credit Default Swap Indices [Member]
Credit Derivatives [Line Items]
Notional Amount		478
Average Term (Years)		2 years 9 months 4 days
Payment / Performance Risk		1.87%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 14	$ 23	$ 23
Average Term (Years)	5 years 6 months 7 days	5 years 5 months 23 days	5 years 4 months 6 days
Payment / Performance Risk	10.31%	9.74%	10.77%