Contingencies, Commitments and Guarantees (details) - Commitments - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Contingencies and Commitments disclosure
Unfunded commitments to private equity limited partnerships and real estate partnerships	$ 1,560	$ 1,600

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