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Fair Values of Financial Instruments - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]      
Percentage of fair value amounts for fixed maturities provided by a pricing service 99.00%cb_PercentageOfFairValueAmountsForFixedMaturitiesProvidedByPricingService 99.00%cb_PercentageOfFairValueAmountsForFixedMaturitiesProvidedByPricingService  
Plan assets at fair value $ 2,946us-gaap_DefinedBenefitPlanFairValueOfPlanAssets $ 2,717us-gaap_DefinedBenefitPlanFairValueOfPlanAssets  
Other Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets at fair value $ 143us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
$ 130us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
$ 96us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember