Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Credit Derivatives [Line Items]
Notional Amount	$ 309	$ 1,239
Average Term (Years)
Payment / Performance Risk
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	23	18
Average Term (Years)	5 years 4 months 6 days	5 years 8 months 27 days
Payment / Performance Risk	10.77%
Payment / Performance Risk		10.89
Single name credit default swaps [Member]
Credit Derivatives [Line Items]
Notional Amount	257	878
Average Term (Years)	2 years 2 months 9 days	2 years 2 months 5 days
Payment / Performance Risk	7.41%	4.98%
Traded credit default swap indices [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 29	$ 343
Average Term (Years)	4 years 11 months 19 days	3 years 2 months 12 days
Payment / Performance Risk	0.77%	4.58%