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Investments (Details) - Other Investments | 9 Months Ended
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Sep. 30, 2025
Investments [Abstract] |
Availability of financial information provided by hedge funds following the date of the reporting | 1 month
Availability of financial information provided by private equity and real estate partnerships following the date of the reporting, maximum | 3 months

X
- Definition Number of months within which financial information provided by hedge funds is available following the reporting date. + References No definition available. + Details
Name: | trv_AvailabilityOfFinancialInformationProvidedByHedgeFunds
Namespace Prefix: | trv_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum number of months before which financial information provided by private equity and real estate partnerships is available following the reporting date. + References No definition available. + Details
Name: | trv_AvailabilityOfFinancialInformationProvidedByPrivateEquityAndRealEstatePartnershipsMaximum
Namespace Prefix: | trv_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration