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Summary of significant accounting policies (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Summary of significant accounting policies [Line Items]        
Deferred Marketing Costs, Amortization Period 10 years      
Deferred marketing costs reported in Deferred policy acquisition costs $ 288ace_AmountOfDeferredMarketingCostsReportedInDeferredPolicyAcquisitionCosts $ 307ace_AmountOfDeferredMarketingCostsReportedInDeferredPolicyAcquisitionCosts    
Amortization expense for deferred marketing costs 99ace_AmortizationExpenseForDeferredMarketingCosts 128ace_AmortizationExpenseForDeferredMarketingCosts 119ace_AmortizationExpenseForDeferredMarketingCosts  
Recoverable from unrated reinsurers, ceded reserve, default factor (percent) 34.00%ace_RecoverableFromUnratedReinsurersCededReserveDefaultFactor      
Reinsurance business assumed 26us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed 27us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed    
Percentage of fair value of loaned securities 102.00%ace_BorrowersCollateralPercentOfFairValueLoanedSecurities      
Maximum overdraft balance guaranteed by ACE Ltd 300ace_MaximumOverdraftBalanceGuaranteed      
Quality assessment threshold used in goodwill impairment testing 50.00%ace_GoodwillImpairmentTestingQualitativeAssessmentPercentageProbability      
Unpaid losses and loss expenses 38,315us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense 37,443us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense 37,946us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense 37,477us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Supplemental Information for Property, Casualty Insurance Underwriters, Reserves for Unpaid Claims and Claims Adjustment Expense 27,008us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense 26,831us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense 26,547us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense  
Gross liability for the amounts due to claimants 606ace_GrossLiabilityForAmountDueToClaimants      
Reinsurance recoverables for amounts due from life insurance companies 557us-gaap_ReinsuranceRecoverables      
Deposit assets reflected in Other assets 89us-gaap_DepositAssets 100us-gaap_DepositAssets    
Reinsurance deposit liabilities included in Deposit liabilities 120us-gaap_DepositContractsLiabilities 131us-gaap_DepositContractsLiabilities    
Contract holder deposit funds included in Deposit liabilities 908ace_ContractHolderDepositFunds 699ace_ContractHolderDepositFunds    
Net operating results of ESIS included within Administrative expenses 27ace_NetOperatingResultsOfEsisIncludedWithinAdministrativeExpenses 25ace_NetOperatingResultsOfEsisIncludedWithinAdministrativeExpenses 23ace_NetOperatingResultsOfEsisIncludedWithinAdministrativeExpenses  
Structured settlements        
Summary of significant accounting policies [Line Items]        
Unpaid losses and loss expenses 49us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis
= ace_ReinsuranceStructuredSettlementsMember		 54us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis
= ace_ReinsuranceStructuredSettlementsMember		    
Discounted Unsettled Claims [Member]        
Summary of significant accounting policies [Line Items]        
Unpaid losses and loss expenses $ 62us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis
= ace_DiscountedUnsettledClaimsMember		 $ 52us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis
= ace_DiscountedUnsettledClaimsMember		    
Minimum        
Summary of significant accounting policies [Line Items]        
Amortization period for value of reinsurance business assumed 9 years      
Finite-lived intangible asset useful life 1 year      
Interest rates used in calculating reserves 1.00%ace_InterestRatesUsedInCalculatingReserves
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		      
Reinsurance Premiums, Amortization Period 1 year      
Maximum        
Summary of significant accounting policies [Line Items]        
Amortization period for value of reinsurance business assumed 40 years      
Finite-lived intangible asset useful life 20 years      
Interest rates used in calculating reserves 6.50%ace_InterestRatesUsedInCalculatingReserves
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		      
Reinsurance Premiums, Amortization Period 3 years