Fair Value Measurements (Details)	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Percent of fixed maturities for which a pricing service estimates fair value	99.00%	99.00%

Percentage of fixed maturities for which a pricing service was used in determining fair value.

No definition available.

Name:	trv_PercentOfFixedMaturitiesForWhichPricingServiceEstimatesFairValue
Namespace Prefix:	trv_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant