Investment Income And Gains And Losses (Net Unrealized Gains (Losses), Including Portion Of Other-Than-Temporary Impairments Included In Other Comprehensive Loss, Reported Within Shareholders' Equity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Deferred income tax provision (benefit)	$ (86)	$ (208)
Unrealized gains (losses), net	(134)	(392)
Total	(220)	(600)
Fixed-Maturity Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Gains	262	208
Losses	(459)	(782)
Foreign exchange	(5)	(14)
Net	(202)	(588)
Other Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Gains	1	10
Losses	(19)	(22)
Net	$ (18)	$ (12)