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SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION | 12 Months Ended
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Dec. 31, 2025
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract] |
SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION | SCHEDUL E III THE HANOVER INSURANCE GROUP, INC. SUPPLEMENTARY INSU RANCE INFORMATION
DECEMBER 31, 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
(in millions) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segments | Deferred acquisition costs |  | Future policy benefits, losses, claims and loss expenses |  | Unearned premiums |  | Other policy claims and benefits payable |  | Premium revenue |  | Net investment income (1) |  | Benefits, claims, losses and settlement expenses |  | Amortization of deferred acquisition costs |  | Other operating expenses (2) |  | Premiums written |
Core Commercial | $ | 234.6 |  | $ | 3,853.1 |  | $ | 1,187.9 |  | $ | 8.3 |  | $ | 2,211.0 |  | $ | 202.5 |  | $ | 1,411.9 |  | $ | 481.2 |  | $ | 274.7 |  | $ | 2,273.7 |
Specialty |  | 227.0 |  |  | 1,725.7 |  |  | 850.8 |  |  | 7.1 |  |  | 1,398.3 |  |  | 102.6 |  |  | 676.9 |  |  | 367.2 |  |  | 165.5 |  |  | 1,441.5 |
Personal Lines |  | 241.4 |  |  | 2,131.4 |  |  | 1,401.7 |  |  | — |  |  | 2,551.8 |  |  | 128.5 |  |  | 1,639.8 |  |  | 436.8 |  |  | 238.6 |  |  | 2,606.9 |
Other |  | — |  |  | 29.6 |  |  | — |  |  | — |  |  | — |  |  | 20.8 |  |  | 0.7 |  |  | — |  |  | 14.1 |  |  | — |
Interest on Debt |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 43.2 |  |  | — |
Eliminations |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Total | $ | 703.0 |  | $ | 7,739.8 |  | $ | 3,440.4 |  | $ | 15.4 |  | $ | 6,161.1 |  | $ | 454.4 |  | $ | 3,729.3 |  | $ | 1,285.2 |  | $ | 736.1 |  | $ | 6,322.1 |
DECEMBER 31, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
(in millions) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segments | Deferred acquisition costs |  | Future policy benefits, losses, claims and loss expenses |  | Unearned premiums |  | Other policy claims and benefits payable |  | Premium revenue |  | Net investment income (1) |  | Benefits, claims, losses and settlement expenses |  | Amortization of deferred acquisition costs |  | Other operating expenses (2) |  | Premiums written |
Core Commercial | $ | 230.8 |  | $ | 3,606.3 |  | $ | 1,121.4 |  | $ | 7.4 |  | $ | 2,148.8 |  | $ | 170.4 |  | $ | 1,302.1 |  | $ | 462.6 |  | $ | 277.9 |  | $ | 2,195.5 |
Specialty |  | 209.2 |  |  | 1,669.1 |  |  | 800.4 |  |  | 6.7 |  |  | 1,322.0 |  |  | 84.5 |  |  | 646.7 |  |  | 347.4 |  |  | 160.6 |  |  | 1,373.9 |
Personal Lines |  | 222.8 |  |  | 2,108.8 |  |  | 1,361.5 |  |  | — |  |  | 2,441.8 |  |  | 106.7 |  |  | 1,807.2 |  |  | 411.7 |  |  | 234.0 |  |  | 2,514.2 |
Other |  | — |  |  | 62.9 |  |  | — |  |  | — |  |  | — |  |  | 11.0 |  |  | 1.4 |  |  | — |  |  | 17.5 |  |  | — |
Interest on Debt |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 34.1 |  |  | — |
Eliminations |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (3.6 | ) |  | — |
Total | $ | 662.8 |  | $ | 7,447.1 |  | $ | 3,283.3 |  | $ | 14.1 |  | $ | 5,912.6 |  | $ | 372.6 |  | $ | 3,757.4 |  | $ | 1,221.7 |  | $ | 720.5 |  | $ | 6,083.6 |
DECEMBER 31, 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
(in millions) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segments | Deferred acquisition costs |  | Future policy benefits, losses, claims and loss expenses |  | Unearned premiums |  | Other policy claims and benefits payable |  | Premium revenue |  | Net investment income (1) |  | Benefits, claims, losses and settlement expenses |  | Amortization of deferred acquisition costs |  | Other operating expenses (2) |  | Premiums written |
Core Commercial | $ | 223.0 |  | $ | 3,461.5 |  | $ | 1,066.8 |  | $ | 6.9 |  | $ | 2,060.3 |  | $ | 151.8 |  | $ | 1,354.9 |  | $ | 443.8 |  | $ | 250.9 |  | $ | 2,107.0 |
Specialty |  | 193.6 |  |  | 1,619.6 |  |  | 755.1 |  |  | 5.9 |  |  | 1,274.2 |  |  | 71.1 |  |  | 645.5 |  |  | 329.5 |  |  | 133.2 |  |  | 1,293.3 |
Personal Lines |  | 204.2 |  |  | 2,148.8 |  |  | 1,280.6 |  |  | — |  |  | 2,328.6 |  |  | 96.8 |  |  | 2,131.9 |  |  | 402.7 |  |  | 211.6 |  |  | 2,409.9 |
Other |  | — |  |  | 65.4 |  |  | — |  |  | — |  |  | — |  |  | 12.4 |  |  | 2.3 |  |  | — |  |  | 20.1 |  |  | — |
Interest on Debt |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 34.1 |  |  | — |
Eliminations |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (8.1 | ) |  | — |
Total | $ | 620.8 |  | $ | 7,295.3 |  | $ | 3,102.5 |  | $ | 12.8 |  | $ | 5,663.1 |  | $ | 332.1 |  | $ | 4,134.6 |  | $ | 1,176.0 |  | $ | 641.8 |  | $ | 5,810.2 |
(1) The Company manages investment assets for its Core Commercial, Specialty, Personal Lines and Other segments on a combined basis, based on the requirements of its combined insurance companies. Net investment income is allocated to these segments based on actuarial information related to the underlying businesses. (2) For other operating expenses that are not directly attributable to a single segment, expenses are allocated using a consistent and reasonable approach, generally based on net premiums earned.

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- Definition The entire disclosure for supplementary insurance information by segment. Includes, but is not limited to, deferred policy acquisition cost; future policy benefit, loss, claim and loss expenses; unearned premium; other policy claim and benefit payable; premium revenue; net investment income; benefit, claim, loss and settlement expenses; amortization of deferred policy acquisition cost; other operating expense; and premium written. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 16 -Paragraph Column J -Footnote 3 -Publisher SEC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 16 -Paragraph Column G -Footnote 3 -Publisher SEC Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16(Column G)(Footnote 3)) -SubTopic 235 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477965/944-235-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16(Column J)(Footnote 3)) -SubTopic 235 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477965/944-235-S99-1 + Details
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