Invested Assets and Related Income - Realized Investment Gains and Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fixed maturities, Gross realized gains	$ 124	$ 70	$ 98
Fixed maturities, Gross realized losses	(20)	(39)	(26)
Fixed maturities, Other-than-temporary impairment losses	(5)	(1)	(5)
Total fixed maturities	99	30	67
Equity securities, Gross realized gains	68	74	50
Equity securities, Gross realized losses		(1)	(1)
Equity securities, Other-than-temporary impairment losses	(40)	(22)	(6)
Total equity securities	28	51	43
Other invested assets	66	207	316
Total Realized Investment Gains, Net	$ 193	$ 288	$ 426