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Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2026 | Mar. 31, 2025
Segment Reporting Information [Line Items] |  |
Earnings before realized gains and income taxes | $ 257 | $ 194
Realized gains (losses) on securities | (18) | 3
Earnings before income taxes | 239 | 197
Operating segments | Property and Casualty Insurance |  |
Segment Reporting Information [Line Items] |  |
Property and casualty insurance underwriting | 156 | 94
Investment and other income, net | 153 | 152
Earnings before realized gains and income taxes | 309 | 246
Operating segments | Property and Casualty Insurance | Property and transportation |  |
Segment Reporting Information [Line Items] |  |
Property and casualty insurance underwriting | 65 | 37
Operating segments | Property and Casualty Insurance | Specialty casualty |  |
Segment Reporting Information [Line Items] |  |
Property and casualty insurance underwriting | 34 | 20
Operating segments | Property and Casualty Insurance | Specialty financial |  |
Segment Reporting Information [Line Items] |  |
Property and casualty insurance underwriting | 57 | 37
Operating segments | Other |  |
Segment Reporting Information [Line Items] |  |
Earnings before realized gains and income taxes | $ (52) | $ (52)

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