Consolidating Financial Statements (Unaudited) (Details) $ in Millions	Mar. 31, 2018 USD ($)
Consolidating Financial Statements of The Travelers Companies, Inc. and Subsidiaries (Unaudited) disclosure
Amount of certain debt obligations of Travelers Property Casualty Corp. (TPC) and Travelers Insurance Group Holdings, Inc. (TIGHI) that are unconditionally guaranteed by The Travelers Companies, Inc.	$ 700

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

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant