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) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Deferred income tax provision (benefit)	$ (20)	$ (86)
Unrealized gains (losses), net	17	(134)
Total	(3)	(220)
Fixed-Maturity Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Gains	252	262
Losses	(278)	(459)
Foreign exchange	21	(5)
Net	(5)	(202)
Other Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Gains	2	1
Losses		(19)
Net	$ 2	$ (18)