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Investment gains/losses and other-than-temporary impairment losses - Other-than-temporary impairment losses (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Schedule of Other than Temporary Impairments [Line Items]      
Other-than-temporary investment losses $ 908 $ 1,973 $ 3,155
Equity Securities [Member]
     
Schedule of Other than Temporary Impairments [Line Items]      
Other-than-temporary investment losses 506 953 3,127
Fixed Maturities [Member]
     
Schedule of Other than Temporary Impairments [Line Items]      
Other-than-temporary investment losses $ 402 $ 1,020 $ 28