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v3.25.3

Fair Value Measurements (Details) | Sep. 30, 2025 | Dec. 31, 2024
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Fair Value Disclosures [Abstract] |  |
Percent of fixed maturities for which a pricing service estimates fair value | 99.00% | 99.00%

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- Definition Percentage of fixed maturities for which a pricing service was used in determining fair value. + References No definition available. + Details
Name: | trv_PercentOfFixedMaturitiesForWhichPricingServiceEstimatesFairValue
Namespace Prefix: | trv_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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