Document And Entity Information |
Apr. 29, 2026 |
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| Cover [Abstract] | |
| Entity Registrant Name | HANOVER INSURANCE GROUP, INC. |
| Amendment Flag | false |
| Entity Central Index Key | 0000944695 |
| Document Type | 8-K |
| Document Period End Date | Apr. 29, 2026 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-13754 |
| Entity Tax Identification Number | 04-3263626 |
| Entity Address, Address Line One | 440 Lincoln Street |
| Entity Address, City or Town | Worcester |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01653 |
| City Area Code | (508) |
| Local Phone Number | 855-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Security 12b Title | Common Stock, $.01 par value |
| Trading Symbol | THG |
| Security Exchange Name | NYSE |
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- Definition For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD. No definition available.
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- Definition Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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