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Investment gains/losses and other-than-temporary impairment losses on investments - Other-than-temporary impairment losses (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Schedule of Other than Temporary Impairments [Line Items]    
Other-than-temporary investment losses $ 337 $ 506
Equity Securities [Member]
   
Schedule of Other than Temporary Impairments [Line Items]    
Other-than-temporary investment losses   506
Fixed Maturities [Member]
   
Schedule of Other than Temporary Impairments [Line Items]    
Other-than-temporary investment losses $ 337