Name:	trv_DebtSecuritiesAvailableForSaleCreditImpairmentChargesIntentToSellNoAllowancePreviouslyRecordedRecognizedInNetRealizedInvestmentGainsLosses
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Data Type:	xbrli:monetaryItemType
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Credit losses recognized in earnings during the period related to debt securities held, as a percentage of the fixed maturity portfolio on a pretax basis.

No definition available.

Name:	trv_DebtSecuritiesAvailableForSaleCreditLossesRecognizedInEarningsForThePeriodAsPercentageOfFixedMaturityPortfolioOnPretaxBasis
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Data Type:	dtr-types:percentItemType
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Credit losses recognized in earnings during the period related to debt securities held, as a percentage of shareholders' equity on an after-tax basis.

No definition available.

Name:	trv_DebtSecuritiesAvailableForSaleCreditLossesRecognizedInEarningsForThePeriodAsPercentageOfShareholdersEquityOnAfterTaxBasis
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Data Type:	dtr-types:percentItemType
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Total amount of credit impairment charges on debt securities included in net realized investment gains (losses) in the consolidated statement of income (loss).

No definition available.

Name:	trv_DebtSecuritiesAvailableForSaleTotalCreditImpairmentChargesRecognizedInNetRealizedInvestmentGainsLosses
Namespace Prefix:	trv_
Data Type:	xbrli:monetaryItemType
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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Name:	us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

Name:	us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of expense (reversal of expense) for allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Data Type:	xbrli:stringItemType
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Name:	us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amount of decrease in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from intent to sell or more likely than not will be required to sell before recovery of amortized cost basis.