Name:	trv_NetFavorablePriorYearReserveDevelopmentImpactingResultsOfOperations
Namespace Prefix:	trv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 420
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481639/420-10-35-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 420
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482017/420-10-50-1

Name:	us-gaap_AccretionExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The increase (decrease) during the reporting period in asbestos and environmental claims reserve, net of reinsurance recoveries.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b),(c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

Name:	us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNetPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

Name:	us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_NoncatastrophicEventAxis=us-gaap_AsbestosIssueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ProductOrServiceAxis=us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=trv_BusinessAndInternationalInsuranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=trv_BondAndSpecialtyInsuranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: