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Investments (details) - Investment Information (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Investment disclosure details      
Fixed maturities, amortized cost $ 60,801us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis $ 62,196us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis  
Fixed maturities, at fair value 63,474us-gaap_AvailableForSaleSecuritiesDebtSecurities 63,956us-gaap_AvailableForSaleSecuritiesDebtSecurities  
Equity securities, cost 579us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis 686us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis  
Equity securities, at fair value 899us-gaap_AvailableForSaleSecuritiesEquitySecurities 943us-gaap_AvailableForSaleSecuritiesEquitySecurities  
Continuous unrealized loss position less than 12 months, fair value 2,744us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 13,836us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue  
Continuous unrealized loss position less than 12 months, gross unrealized losses 46us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss 592us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss  
Continuous unrealized loss position 12 months or longer, fair value 3,536us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 875us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue  
Continuous unrealized loss position 12 months or longer, gross unrealized losses 78us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 111us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss  
Continuous unrealized loss position, total, fair value 6,280us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue 14,711us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue  
Continuous unrealized loss position, total, gross unrealized losses 124us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss 703us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss  
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less 4trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostThreeMonthsOrLess    
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less 2trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanSixMonthsTwelveMonthsOrLess    
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months 2trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanTwelveMonths    
Available-for-sale securities for which fair value is less than 80% of amortized cost, total 8trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostTotal    
Maxiumum [Member]      
Investment disclosure details      
Unrealized investment losses for securities for which fair value is less than 80% of amortized cost, as a percentage of the combined fixed maturity and equity security portfolios on a pretax basis 1.00%trv_UnrealizedInvestmentLossesAsPercentageOfCombinedFixedMaturityAndEquitySecurityPortfoliosOnPretaxBasis
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Unrealized investment losses for securities for which fair value is less than 80% of amortized cost, as a percentage of shareholders' equity on an after-tax basis 1.00%trv_UnrealizedInvestmentLossesAsPercentageOfShareholdersEquityOnAfterTaxBasis
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Fixed maturities [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 60,801us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
62,196us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Gross unrealized gains 2,791us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
2,460us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Gross unrealized losses 118us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
700us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Fixed maturities, at fair value 63,474us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
63,956us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Gross realized gains 44us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
66us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
70us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
Gross realized losses 12us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
25us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
9us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
Continuous unrealized loss position less than 12 months, fair value 2,619us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
13,636us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 41us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
589us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, fair value 3,493us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
875us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, gross unrealized losses 77us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
111us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Continuous unrealized loss position, total, fair value 6,112us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
14,511us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Continuous unrealized loss position, total, gross unrealized losses 118us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
700us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less 4trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostThreeMonthsOrLess
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less 2trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanSixMonthsTwelveMonthsOrLess
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months 2trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanTwelveMonths
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, total 8trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostTotal
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
   
Fixed maturities [Member] | Below investment grade [Member]      
Investment disclosure details      
Fixed maturities, at fair value 1,910us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
1,930us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_DebtSecuritiesMember
 
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 2,022us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
2,288us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Gross unrealized gains 36us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
39us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Gross unrealized losses 5us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
12us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Fixed maturities, at fair value 2,053us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
2,315us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Continuous unrealized loss position less than 12 months, fair value 180us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
433us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 2us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
12us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Continuous unrealized loss position 12 months or longer, fair value 125us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
   
Continuous unrealized loss position 12 months or longer, gross unrealized losses 3us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
   
Continuous unrealized loss position, total, fair value 305us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
433us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Continuous unrealized loss position, total, gross unrealized losses 5us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
12us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Obligations of states, municipalities and political subdivisions [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 31,895us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
34,488us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Gross unrealized gains 1,688us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
1,436us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Gross unrealized losses 10us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
362us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Fixed maturities, at fair value 33,573us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
35,562us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position less than 12 months, fair value 173us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
4,785us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
298us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position 12 months or longer, fair value 797us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
432us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position 12 months or longer, gross unrealized losses 9us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
64us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position, total, fair value 970us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
5,217us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Continuous unrealized loss position, total, gross unrealized losses 10us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
362us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 7,229us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
9,074us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
 
Gross unrealized gains 332us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
445us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
 
Gross unrealized losses   1us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
 
Fixed maturities, at fair value 7,561us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
9,518us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsPreRefundedMember
 
Obligations of states, municipalities and political subdivisions, all other (not pre-refunded) [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 24,666us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
25,414us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
 
Gross unrealized gains 1,356us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
991us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
 
Gross unrealized losses 10us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
361us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
 
Fixed maturities, at fair value 26,012us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
26,044us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_USStatesAndPoliticalSubdivisionsAllOtherMember
 
Debt securities issued by foreign governments [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 2,320us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
2,552us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Gross unrealized gains 48us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
33us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Gross unrealized losses   8us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Fixed maturities, at fair value 2,368us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
2,577us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Continuous unrealized loss position less than 12 months, fair value 50us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
907us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses   8us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, fair value 24us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Continuous unrealized loss position, total, fair value 74us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
908us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Continuous unrealized loss position, total, gross unrealized losses   8us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 2,052us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
2,263us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Gross unrealized gains 165us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
179us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Gross unrealized losses 4us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
18us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Fixed maturities, at fair value 2,213us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
2,424us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position less than 12 months, fair value 68us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
542us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses   17us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, fair value 192us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
21us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, gross unrealized losses 4us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position, total, fair value 260us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
563us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Continuous unrealized loss position, total, gross unrealized losses 4us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
18us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Residential mortgage-backed pass-through securities classified as available-for-sale, GNMA, FNMA, FHLMC and Canadian Government [Member]      
Investment disclosure details      
Fixed maturities, at fair value 872us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_MortgageBackedSecuritiesIssuedByUSOrCADGovernmentSponsoredEnterprisesMember
1,070us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_MortgageBackedSecuritiesIssuedByUSOrCADGovernmentSponsoredEnterprisesMember
 
Residential collateralized mortgage obligations [Member]      
Investment disclosure details      
Fixed maturities, at fair value 1,340us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CollateralizedDebtObligationsMember
1,360us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CollateralizedDebtObligationsMember
 
Percent guaranteed by or fully collateralized by securities issued by GNMA, FNMA or FHLMC 46.00%trv_PercentGuaranteedByOrFullyCollateralizedBySecuritiesIssuedByGnmaFnmaOrFhlmc
/ us-gaap_InvestmentTypeAxis
= us-gaap_CollateralizedDebtObligationsMember
42.00%trv_PercentGuaranteedByOrFullyCollateralizedBySecuritiesIssuedByGnmaFnmaOrFhlmc
/ us-gaap_InvestmentTypeAxis
= us-gaap_CollateralizedDebtObligationsMember
 
Non-guaranteed residential collateralized mortgage obligations [Member]      
Investment disclosure details      
Fixed maturities, at fair value 725us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_NonGuaranteedCollateralizedDebtObligationsMember
790us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_NonGuaranteedCollateralizedDebtObligationsMember
 
All other corporate bonds [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 22,390us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
20,472us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Gross unrealized gains 844us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
767us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Gross unrealized losses 99us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
299us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Fixed maturities, at fair value 23,135us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
20,940us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position less than 12 months, fair value 2,148us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
6,887us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 38us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
253us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, fair value 2,355us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
421us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position 12 months or longer, gross unrealized losses 61us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
46us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position, total, fair value 4,503us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
7,308us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Continuous unrealized loss position, total, gross unrealized losses 99us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
299us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_OtherDebtSecuritiesMember
 
Commercial mortgage-backed securities [Member]      
Investment disclosure details      
Fixed maturities, at fair value 715us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
475us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Commercial mortgage-backed securities, containing guarantees by the U.S. government or a government-sponsored enterprise [Member]      
Investment disclosure details      
Fixed maturities, at fair value 202us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_CommercialMortgageBackedSecuritiesContainingGuaranteesByUSGovernmentOrGovernmentSponsoredEnterpriseMember
59us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_CommercialMortgageBackedSecuritiesContainingGuaranteesByUSGovernmentOrGovernmentSponsoredEnterpriseMember
 
Commercial mortgage-backed securities, non-guaranteed securities [Member]      
Investment disclosure details      
Fixed maturities, at fair value 513us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_CommercialMortgageBackedSecuritiesNonGuaranteedSecuritiesMember
416us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= trv_CommercialMortgageBackedSecuritiesNonGuaranteedSecuritiesMember
 
Other fixed maturities [Member]      
Investment disclosure details      
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less 4trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostThreeMonthsOrLess
/ us-gaap_InvestmentTypeAxis
= trv_FixedMaturitiesExcludingMortgageBackedSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less 2trv_AvailableForSaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanSixMonthsTwelveMonthsOrLess
/ us-gaap_InvestmentTypeAxis
= trv_FixedMaturitiesExcludingMortgageBackedSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months 2trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostGreaterThanTwelveMonths
/ us-gaap_InvestmentTypeAxis
= trv_FixedMaturitiesExcludingMortgageBackedSecuritiesMember
   
Available-for-sale securities for which fair value is less than 80% of amortized cost, total 8trv_AvailableforsaleSecuritiesForWhichFairValueIsLessThanEightyPercentOfAmortizedCostTotal
/ us-gaap_InvestmentTypeAxis
= trv_FixedMaturitiesExcludingMortgageBackedSecuritiesMember
   
Redeemable preferred stock [Member]      
Investment disclosure details      
Fixed maturities, amortized cost 122us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
133us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Gross unrealized gains 10us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
6us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Gross unrealized losses   1us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Fixed maturities, at fair value 132us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
138us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Continuous unrealized loss position less than 12 months, fair value   82us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses   1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Continuous unrealized loss position, total, fair value   82us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Continuous unrealized loss position, total, gross unrealized losses   1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_RedeemablePreferredStockMember
 
Equity securities [Member]      
Investment disclosure details      
Equity securities, cost 579us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
686us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Gross unrealized gains 326us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
260us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Gross unrealized losses 6us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
3us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Equity securities, at fair value 899us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
943us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Gross realized gains 27us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
16us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
8us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
Gross realized losses 3us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
1us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Continuous unrealized loss position less than 12 months, fair value 125us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
200us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 5us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
3us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Continuous unrealized loss position 12 months or longer, fair value 43us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
   
Continuous unrealized loss position 12 months or longer, gross unrealized losses 1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
   
Continuous unrealized loss position, total, fair value 168us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
200us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Continuous unrealized loss position, total, gross unrealized losses 6us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
3us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
 
Equity securities [Member] | Maxiumum [Member]      
Investment disclosure details      
Gross realized losses     1us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Public common stock [Member]      
Investment disclosure details      
Equity securities, cost 400us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
385us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Gross unrealized gains 295us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
226us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Gross unrealized losses 4us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
1us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Equity securities, at fair value 691us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
610us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Continuous unrealized loss position less than 12 months, fair value 81us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
53us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 4us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Continuous unrealized loss position 12 months or longer, fair value 1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
   
Continuous unrealized loss position, total, fair value 82us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
53us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Continuous unrealized loss position, total, gross unrealized losses 4us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommonStockMember
 
Non-redeemable preferred stock [Member]      
Investment disclosure details      
Equity securities, cost 179us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
301us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Gross unrealized gains 31us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
34us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Gross unrealized losses 2us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
2us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Equity securities, at fair value 208us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
333us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Continuous unrealized loss position less than 12 months, fair value 44us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
147us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Continuous unrealized loss position less than 12 months, gross unrealized losses 1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
2us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Continuous unrealized loss position 12 months or longer, fair value 42us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
   
Continuous unrealized loss position 12 months or longer, gross unrealized losses 1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
   
Continuous unrealized loss position, total, fair value 86us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
147us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Continuous unrealized loss position, total, gross unrealized losses 2us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
2us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_NonredeemablePreferredStockMember
 
Real estate [Member]      
Investment disclosure details      
Gross realized gains 6us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember
7us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember
19us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember
Gross realized losses $ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember
$ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember
$ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateInvestmentMember