Pension Plans, Retirement Benefits and Savings Plans (details) - Additional Pension Disclosures - Change in Assumptions for Pension Plans and Postretirement Benefit Plans [Member] $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)
Impact of Change in Estimation Approach [Member]
Change in Accounting Estimate
Reduction to service cost	$ 2	$ 3
Reduction to interest cost	$ 7	$ 15
Current Estimation Approach [Member] \| Qualified Domestic Pension Plan [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	4.77%	4.77%
Weighted average discount rate used to measure interest cost (percent)	3.64%	3.64%
Current Estimation Approach [Member] \| Nonqualified Domestic Pension Plan [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	4.53%	4.53%
Weighted average discount rate used to measure interest cost (percent)	3.47%	3.47%
Current Estimation Approach [Member] \| Domestic Postretirement Benefit Plans [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	0.00%	0.00%
Weighted average discount rate used to measure interest cost (percent)	3.53%	3.53%
Prior Estimation Approach [Member] \| Qualified Domestic Pension Plan [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	4.50%	4.50%
Weighted average discount rate used to measure interest cost (percent)	4.50%	4.50%
Prior Estimation Approach [Member] \| Nonqualified Domestic Pension Plan [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	4.37%	4.37%
Weighted average discount rate used to measure interest cost (percent)	4.37%	4.37%
Prior Estimation Approach [Member] \| Domestic Postretirement Benefit Plans [Member]
Change in Accounting Estimate
Weighted average discount rate used to measure service cost (percent)	4.35%	4.35%
Weighted average discount rate used to measure interest cost (percent)	4.35%	4.35%

The interest rate used to adjust for the time value of money for the plan, used for interest cost.

No definition available.

Name:	trv_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRateInterestCost
Namespace Prefix:	trv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The interest rate used to adjust for the time value of money for the plan, used for service cost.

+ References

No definition available.

+ Details

Name:	trv_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRateServiceCost
Namespace Prefix:	trv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

+ Details

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

- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Service Cost (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6525008

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

+ Details

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

- Details

Name:	us-gaap_ChangeInAccountingEstimateByTypeAxis=us-gaap_ChangeInAssumptionsForPensionPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=trv_ImpactOfChangeInEstimationApproachMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=trv_CurrentEstimationApproachMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=trv_QualifiedDomesticPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=trv_NonqualifiedDomesticPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioPreviouslyReportedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: