Contingencies, Commitments and Guarantees (Details) - Commitments - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Contingencies, Commitments and Guarantees [Abstract]
Unfunded commitments to private equity limited partnerships, real estate partnerships and other parties	$ 1,700	$ 1,410

The amount of unfunded commitments to private equity limited partnerships and real estate partnerships in which the Company invests.

No definition available.

Name:	trv_UnfundedCommitmentsToPrivateEquityLimitedPartnershipsRealEstatePartnershipsAndOther
Namespace Prefix:	trv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant