Invested Assets - Realized Investment Gains and Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule of Available-For-Sale Securities [Line Items]
Fixed maturities, Gross realized gains	$ 35	$ 25	$ 97	$ 48
Fixed maturities, Gross realized losses	(8)	(10)	(18)	(25)
Fixed maturities, Other-than-temporary impairment losses	(2)	(1)	(4)	(1)
Total fixed maturities	25	14	75	22
Equity securities, Gross realized gains	25	16	50	45
Equity securities, Gross realized losses				(1)
Equity securities, Other-than-temporary impairment losses	(5)	(6)	(40)	(22)
Total equity securities	20	10	10	22
Other invested assets	(45)	47	18	256
Total Realized Investment Gains, Net		$ 71	$ 103	$ 300