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Segment Information - Schedule of Return on Equity (Details) | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting Information [Line Items] |  |  |
ROE | 7.00% | 14.30% | 8.80%
Operating Segments | Total Insurance Operations |  |  |
Segment Reporting Information [Line Items] |  |  |
ROE | (3.70%) | 4.20% | 5.40%
Operating Segments | Standard Commercial Lines |  |  |
Segment Reporting Information [Line Items] |  |  |
ROE | (4.00%) | 5.00% | 4.60%
Operating Segments | Standard Personal Lines |  |  |
Segment Reporting Information [Line Items] |  |  |
ROE | (1.10%) | (2.50%) | (0.20%)
Operating Segments | E&S Lines |  |  |
Segment Reporting Information [Line Items] |  |  |
ROE | 1.40% | 1.70% | 1.00%
Operating Segments | Investments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment income earned | 12.80% | 12.40% | 9.40%
Net realized and unrealized investment gains (losses) | (0.10%) | (0.10%) | (3.60%)
ROE | 12.70% | 12.30% | 5.80%
Reconciling Item, Corporate |  |  |
Segment Reporting Information [Line Items] |  |  |
ROE | (2.00%) | (2.20%) | (2.40%)

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