Investments (Net Realized Gains (Losses) And Losses Included In Net Realized Gains (Losses) And Other Comprehensive Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments, Debt and Equity Securities [Abstract]
OTTI on fixed maturities, gross									$ (26)	$ (61)	$ (115)
OTTI on fixed maturities recognized in OCI (pre-tax)									1	15	69
OTTI on fixed maturities, net									(25)	(46)	(46)
Fixed maturities, Gross realized gains excluding OTTI									388	410	569
Fixed maturities, Gross realized losses excluding OTTI									(133)	(200)	(143)
Total fixed maturities									230	164	380
OTTI on equity securities									(5)	(1)	0
Equity securities, Gross realized gains excluding OTTI									11	15	86
Equity securities, Gross realized losses excluding OTTI									(2)	(5)	(2)
Total equity securities									4	9	84
OTTI on other investments									(7)	3	(13)
Foreign exchange losses									(16)	(13)	(54)
Investment and embedded derivative instruments									(6)	(143)	58
Fair value adjustments on insurance derivative									171	(779)	(28)
S&P put options and futures									(297)	(4)	(150)
Other derivative instruments									(4)	(4)	(19)
Other									3	(22)	174
Total net realized gains (losses)	272	(60)	(394)	260	83	(760)	(73)	(45)	78	(795)	432
Change in net unrealized appreciation (depreciation) on investments, Fixed maturities available for sale									1,099	569	451
Change in net unrealized appreciation (depreciation) on investments, Fixed maturities held to maturity									(94)	(89)	522
Change in net unrealized appreciation (depreciation) on investments, Equity securities									61	(47)	(44)
Change in net unrealized appreciation (depreciation) on investments, Other									50	40	(35)
Change in net unrealized appreciation (depreciation) on investments, Income tax expense									(198)	(157)	(152)
Change in net unrealized appreciation on investments,									918	316	742
Total net realized gains (losses) and change in net unrealized appreciation (depreciation) on investments									$ 996	$ (479)	$ 1,174