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Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |  |
Deferred Acquisition Costs |  | $ 1,734 | $ 1,531 | $ 1,263
Reserves for Losses and Loss Adjustment Expenses |  | 29,369 | 22,752 | 20,032
Unearned Premiums |  | 10,218 | 8,808 | 7,337
Net Premiums Earned |  | 15,100 | 12,440 | 9,679
Net Losses and Loss Adjustment Expenses Incurred |  | 8,342 | 6,246 | 5,028
Amortization of Deferred Acquisition Costs |  | 2,651 | 2,312 | 1,740
Other Operating Expenses | [1] | 1,472 | 1,301 | 1,128
Net Premiums Written |  | 15,732 | 13,468 | 11,078
Operating segments | Insurance |  |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |  |
Deferred Acquisition Costs |  | 696 | 566 | 301
Reserves for Losses and Loss Adjustment Expenses |  | 16,277 | 12,250 | 11,017
Unearned Premiums |  | 4,857 | 3,917 | 3,382
Net Premiums Earned |  | 6,627 | 5,446 | 4,560
Net Losses and Loss Adjustment Expenses Incurred |  | 4,070 | 3,122 | 2,784
Amortization of Deferred Acquisition Costs |  | 1,217 | 1,055 | 887
Other Operating Expenses | [1] | 995 | 819 | 665
Net Premiums Written |  | 6,874 | 5,862 | 5,021
Operating segments | Reinsurance |  |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |  |
Deferred Acquisition Costs |  | 981 | 901 | 992
Reserves for Losses and Loss Adjustment Expenses |  | 12,567 | 9,924 | 8,306
Unearned Premiums |  | 4,891 | 4,254 | 3,206
Net Premiums Earned |  | 7,242 | 5,836 | 3,959
Net Losses and Loss Adjustment Expenses Incurred |  | 4,327 | 3,227 | 2,568
Amortization of Deferred Acquisition Costs |  | 1,432 | 1,240 | 813
Other Operating Expenses | [1] | 270 | 288 | 268
Net Premiums Written |  | 7,746 | 6,554 | 4,924
Operating segments | Mortgage |  |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |  |
Deferred Acquisition Costs |  | 57 | 64 | (30)
Reserves for Losses and Loss Adjustment Expenses |  | 525 | 578 | 709
Unearned Premiums |  | 470 | 637 | 749
Net Premiums Earned |  | 1,231 | 1,158 | 1,160
Net Losses and Loss Adjustment Expenses Incurred |  | (55) | (103) | (324)
Amortization of Deferred Acquisition Costs |  | 2 | 17 | 40
Other Operating Expenses | [1] | 207 | 194 | 195
Net Premiums Written |  | $ 1,112 | $ 1,052 | $ 1,133
[1] | Certain other operating expenses relate to the Company’s corporate items. Such amounts are not reflected in the table above. See note 4, “Segment Information,” to our consolidated financial statements in Item 8 for information

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