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Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting Information [Line Items] |  |  |
Net investment income | $ 780 | $ 742 | $ 717
Other income | 124 | 146 | 117
Revenues before realized gains (losses) | 8,324 | 7,867 | 7,156
Realized gains (losses) on securities | 0 | (36) | (116)
Realized loss on subsidiary | 0 | (4) | 0
Total revenues | 8,324 | 7,827 | 7,040
Property and casualty insurance | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net earned premiums | 7,036 | 6,531 | 6,085
Net investment income | 784 | 729 | 683
Other income | 8 | 16 | 12
Revenues before realized gains (losses) | 7,828 | 7,276 | 6,780
Other | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues before realized gains (losses) | 496 | 591 | 376
Property and transportation | Property and casualty insurance | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net earned premiums | 2,793 | 2,519 | 2,487
Specialty casualty | Property and casualty insurance | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net earned premiums | 2,967 | 2,886 | 2,659
Specialty financial | Property and casualty insurance | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net earned premiums | 1,032 | 867 | 698
Other specialty | Property and casualty insurance | Operating segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Net earned premiums | $ 244 | $ 259 | $ 241

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