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Claim and Claim Adjustment Expense Reserves - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Liability for Claims and Claims Adjustment Expense [Abstract]    
Catastrophe losses, net of reinsurance $ 29l_CatastropheLossesNetOfReinsurance $ 74l_CatastropheLossesNetOfReinsurance