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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
Sep. 30, 2012
Dec. 31, 2011
Schedule of Investments [Line Items]    
Total $ 163 $ (220)
Deferred income tax provision (benefit) 35 (86)
Unrealized gains (losses), net 128 (134)
Fixed-Maturity Investments [Member]
    
Schedule of Investments [Line Items]    
Gains 337 262
Losses (191) (459)
Foreign exchange 17 (5)
Net 163 (202)
Other Investments [Member]
    
Schedule of Investments [Line Items]    
Gains   1
Losses   (19)
Net   $ (18)