Amount awarded from other party to the entity in judgment or settlement of litigation.

No definition available.

Name:	trv_LitigationSettlementAmountAwardedFromOtherParty1
Namespace Prefix:	trv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of other reinsurers against which judgment was entered in a reinsurance dispute.

+ References

No definition available.

+ Details

Name:	trv_NumberOfAdditionalPartiesAgainstWhichJudgmentWasEnteredInDispute
Namespace Prefix:	trv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of discrete issues for which the Court of Appeals remanded the case for trial.

+ References

No definition available.

+ Details

Name:	trv_NumberOfDiscreteIssuesModifiedInPartBySummaryJudgmentInDispute
Namespace Prefix:	trv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of reinsurers with whom the Company has reached a settlement agreement.

+ References

No definition available.

+ Details

Name:	trv_NumberOfReinsurersWithWhomCompanyHasReachedSettlementAgreement
Namespace Prefix:	trv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Cash received for the settlement of litigation during the current period, after-tax.

+ References

No definition available.

+ Details

Name:	trv_ProceedsFromLegalSettlementsAfterTax
Namespace Prefix:	trv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

Name:	us-gaap_GainLossRelatedToLitigationSettlement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Interest expense (income) directly attributable to an award in settlement of litigation.

+ References

No definition available.

+ Details

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

- Definition

Cash received for the settlement of litigation during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

+ Details

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

- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387

+ Details

Name:	us-gaap_ReinsuranceRecoverablesOnPaidAndUnpaidLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_GainContingenciesByNatureAxis=trv_UnitedStatesFidelityAndGuarantyCompanyVAmericanReInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Contingencies, Commitments and Guarantees (details) $ in Millions	3 Months Ended	79 Months Ended
	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	May 01, 2017 item	Nov. 07, 2016 USD ($) item	Nov. 06, 2016 USD ($)	Aug. 17, 2010 item
Gain Contingency
Reinsurance recoverables	$ 8,287		$ 8,345
United States Fidelity & Guaranty Company v. American Re-Insurance Company, et al. [Member]
Gain Contingency
Number of discrete issues for which the Court of Appeals remanded the case for trial \| item								2
Number of reinsurer defendants \| item					2	3
Number of reinsurers with whom the Company reached a settlement agreeement \| item					2	1
Gain from payment received from settlement (pre-tax)	126
Gain from payment received from settlement (after-tax)	$ 82
Reinsurance recoverables		$ 31		$ 0		$ 31	$ 238
Total settlement amount		71
Settlement amount, reinsurance recoverables		31
Interest related to settlement award		$ 40