Debt (Details) - Junior Subordinated Debt $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) trusts debenture_instruments	Dec. 31, 2018 USD ($)
Debt Instrument
Unamortized fair value adjustment	$ 43	$ 44
Amount of certain debt obligations of Travelers Property Casualty Corp. (TPC) and Travelers Insurance Group Holdings, Inc. (TIGHI) that are fully and unconditionally guaranteed by The Travelers Companies, Inc.	$ 700
Junior Subordinated Debt [Member]
Debt Instrument
Number of junior subordinated debentures that are all similar in nature \| debenture_instruments	3
Number of separate trusts that issued preferred securities and used proceeds to purchase the Company's subordinated debentures \| trusts	3
Impact of amortization of the fair value adjustment on interest expense	$ 1	$ 2
Junior Subordinated Debt [Member] \| 7.625% Junior subordinated debentures due December 15, 2027 [Member]
Debt Instrument
Interest rate (percent)	7.625%	7.625%
Effective interest rate (percent)	6.147%
Unamortized fair value adjustment	$ 11	$ 12
Junior Subordinated Debt [Member] \| 8.50% Junior subordinated debentures due December 15, 2045 [Member]
Debt Instrument
Interest rate (percent)	8.50%	8.50%
Effective interest rate (percent)	6.362%
Unamortized fair value adjustment	$ 14	$ 14
Junior Subordinated Debt [Member] \| 8.312% Junior subordinated debentures due July 1, 2046 [Member]
Debt Instrument
Interest rate (percent)	8.312%	8.312%
Effective interest rate (percent)	6.362%
Unamortized fair value adjustment	$ 18	$ 18
Senior Notes [Member] \| 7.75% Senior notes due April 15, 2026 [Member]
Debt Instrument
Interest rate (percent)	7.75%	7.75%
Amount of certain debt obligations of Travelers Property Casualty Corp. (TPC) and Travelers Insurance Group Holdings, Inc. (TIGHI) that are fully and unconditionally guaranteed by The Travelers Companies, Inc.	$ 200
Senior Notes [Member] \| 6.375% Senior notes due March 15, 2033 [Member]
Debt Instrument
Interest rate (percent)	6.375%	6.375%
Amount of certain debt obligations of Travelers Property Casualty Corp. (TPC) and Travelers Insurance Group Holdings, Inc. (TIGHI) that are fully and unconditionally guaranteed by The Travelers Companies, Inc.	$ 500

Amount of certain debt obligations of TPC that are unconditionally guaranteed by The Travelers Companies, Inc.

No definition available.

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- Definition

The reduction to interest expense as a result of amortization of the fair value adjustment.

+ References

No definition available.

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- Definition

The number of junior subordinated debentures that re not fixed-to-floating rate debentures.

+ References

No definition available.

+ Details

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- Definition

The number of separate trusts that issued preferred securities and used proceeds to purchase the Company's subordinated debentures that are not fixed-to-floating rate.

+ References

No definition available.

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- Definition

The unamortized adjustment made as a result of the adjustment to fair value for debt assumed in a business combination.

+ References

No definition available.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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- 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.

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