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SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT PARENT COMPANY ONLY (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
The Hanover Insurance Group [Member] |  |  |
Supplementary Insurance Information By Segment [Line Items] |  |  |
Investment assets transferred to the parent company to settle dividend balances | $ 292.7 | $ 25.8 | $ 98.6

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