Investment Income And Gains And Losses (Net Unrealized Gains (Losses), Including Portion Of Other-Than-Temporary Impairments Included In Accumulated Other Comprehensive Income (Loss), Reported Within Shareholders' Equity) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Total	$ 91	$ (220)
Deferred income tax provision (benefit)	18	(86)
Unrealized gains (losses), net	73	(134)
Fixed-Maturity Investments [Member]
Schedule of Investments [Line Items]
Gains	314	262
Losses	(225)	(459)
Foreign exchange	3	(5)
Net	92	(202)
Other Investments [Member]
Schedule of Investments [Line Items]
Gains		1
Losses	(1)	(19)
Net	$ (1)	$ (18)