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Contingencies, Commitments and Guarantees (Details) - Commitments - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Contingencies, Commitments and Guarantees [Abstract] |  |
Unfunded commitments to private equity limited partnerships, real estate partnerships and other investments | $ 1,370 | $ 1,490

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

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- Definition The amount of unfunded commitments to private equity limited partnerships and real estate partnerships in which the Company invests. + References No definition available. + Details
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Namespace Prefix: | trv_
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