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Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | $ 8,295,479 |  | $ 7,587,792 |  | $ 6,503,029 |
Net investment income |  | 734,532 |  | 446,755 |  | 367,417 |
Net investment gains (losses) |  | 1,524,054 |  | (1,595,733) |  | 1,978,534 |
Products revenues |  | 2,545,053 |  | 2,427,096 |  | 1,712,120 |
Services and other revenues |  | 2,704,512 |  | 2,809,425 |  | 2,285,325 |
Total operating revenues |  | 15,803,630 |  | 11,675,335 |  | 12,846,425 |
Losses and loss adjustment expenses, current accident year |  | (5,360,559) |  | (4,613,035) |  | (4,061,000) |
Losses and loss adjustment expenses, prior accident years |  | 38,550 |  | 167,446 |  | 479,795 |
Amortization of policy acquisition costs |  | (1,763,670) |  | (1,655,106) |  | (1,419,266) |
Other underwriting expenses |  | (1,077,064) |  | (860,477) |  | (874,473) |
Products expenses |  | (2,220,676) |  | (2,241,736) |  | (1,544,506) |
Services and other expenses |  | (2,310,769) |  | (2,306,985) |  | (2,024,931) |
Amortization of intangible assets |  | (180,614) | [1] | (178,778) | [2] | (160,539) | [3]
Goodwill, Impairment Loss |  | 0 |  | (80,000) |  | 0 |
Segment profit (loss) |  | 2,928,828 |  | (93,336) |  | 3,241,505 |
Interest expense |  | (185,077) |  | (196,062) |  | (183,579) |
Net foreign exchange gains (losses) |  | (90,045) |  | 137,832 |  | 71,902 |
Income (Loss) Before Income Taxes |  | 2,653,706 |  | (151,566) |  | 3,129,828 |
Insurance [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | 7,282,705 |  | 6,528,263 |  | 5,465,284 |
Net investment income |  | 0 |  | 0 |  | 0 |
Net investment gains (losses) |  | 0 |  | 0 |  | 0 |
Products revenues |  | 0 |  |  |  | 0 |
Services and other revenues |  | 0 |  | 0 |  | 0 |
Total operating revenues |  | 7,282,705 |  | 6,528,263 |  | 5,465,284 |
Losses and loss adjustment expenses, current accident year |  | (4,690,745) |  | (3,936,425) |  | (3,311,185) |
Losses and loss adjustment expenses, prior accident years |  | 104,743 |  | 142,924 |  | 506,292 |
Amortization of policy acquisition costs |  | (1,508,169) |  | (1,375,539) |  | (1,153,049) |
Other underwriting expenses |  | (1,026,358) |  | (809,352) |  | (810,929) |
Products expenses |  | 0 |  | 0 |  | 0 |
Services and other expenses |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3]
Goodwill, Impairment Loss |  |  |  | 0 |  |  |
Segment profit (loss) |  | 162,176 |  | 549,871 |  | 696,413 |
Reinsurance [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | 1,014,294 |  | 1,063,347 |  | 1,042,048 |
Net investment income |  | 0 |  | 0 |  | 0 |
Net investment gains (losses) |  | 0 |  | 0 |  | 0 |
Products revenues |  | 0 |  |  |  | 0 |
Services and other revenues |  | 0 |  | 0 |  | 0 |
Total operating revenues |  | 1,014,294 |  | 1,063,347 |  | 1,042,048 |
Losses and loss adjustment expenses, current accident year |  | (669,814) |  | (676,610) |  | (749,815) |
Losses and loss adjustment expenses, prior accident years |  | (57,081) |  | 26,052 |  | (19,928) |
Amortization of policy acquisition costs |  | (255,501) |  | (279,567) |  | (266,217) |
Other underwriting expenses |  | (51,163) |  | (49,363) |  | (61,326) |
Products expenses |  | 0 |  | 0 |  | 0 |
Services and other expenses |  | 0 |  | 0 |  | 109 |
Amortization of intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3]
Goodwill, Impairment Loss |  |  |  | 0 |  |  |
Segment profit (loss) |  | (19,265) |  | 83,859 |  | (55,129) |
Investing [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | 0 |  | 0 |  | 0 |
Net investment income |  | 729,219 |  | 445,846 |  | 367,406 |
Net investment gains (losses) |  | 1,524,054 |  | (1,595,733) |  | 1,978,534 |
Products revenues |  | 0 |  |  |  | 0 |
Services and other revenues |  | (11,854) |  | (17,661) |  | 7,184 |
Total operating revenues |  | 2,241,419 |  | (1,167,548) |  | 2,353,124 |
Losses and loss adjustment expenses, current accident year |  | 0 |  | 0 |  | 0 |
Losses and loss adjustment expenses, prior accident years |  | 0 |  | 0 |  | 0 |
Amortization of policy acquisition costs |  | 0 |  | 0 |  | 0 |
Other underwriting expenses |  | 0 |  | 0 |  | 0 |
Products expenses |  | 0 |  | 0 |  | 0 |
Services and other expenses |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3]
Goodwill, Impairment Loss |  |  |  | 0 |  |  |
Segment profit (loss) |  | 2,241,419 |  | (1,167,548) |  | 2,353,124 |
Markel Ventures [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | 0 |  | 0 |  | 0 |
Net investment income |  | 5,313 |  | 909 |  | 11 |
Net investment gains (losses) |  | 0 |  | 0 |  | 0 |
Products revenues |  | 2,545,053 |  | 2,427,096 |  | 1,712,120 |
Services and other revenues |  | 2,434,715 |  | 2,329,522 |  | 1,931,696 |
Total operating revenues |  | 4,985,081 |  | 4,757,527 |  | 3,643,827 |
Losses and loss adjustment expenses, current accident year |  | 0 |  | 0 |  | 0 |
Losses and loss adjustment expenses, prior accident years |  | 0 |  | 0 |  | 0 |
Amortization of policy acquisition costs |  | 0 |  | 0 |  | 0 |
Other underwriting expenses |  | 0 |  | 0 |  | 0 |
Products expenses |  | (2,220,676) |  | (2,241,736) |  | (1,544,506) |
Services and other expenses |  | (2,244,527) |  | (2,111,510) |  | (1,769,201) |
Amortization of intangible assets |  | (82,370) | [1] | (79,043) | [2] | (57,568) | [3]
Goodwill, Impairment Loss |  |  |  | 0 |  |  |
Segment profit (loss) |  | 437,508 |  | 325,238 |  | 272,552 |
Interest expense | [4] | (47,227) |  | (46,780) |  | (35,031) |
Other [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Earned premiums |  | (1,520) | [5] | (3,818) | [6] | (4,303) | [7]
Net investment income |  | 0 | [5] | 0 | [6] | 0 | [7]
Net investment gains (losses) |  | 0 | [5] | 0 | [6] | 0 | [7]
Products revenues |  | 0 | [5] |  |  | 0 | [7]
Services and other revenues |  | 281,651 | [5] | 497,564 | [6] | 346,445 | [7]
Total operating revenues |  | 280,131 |  | 493,746 |  | 342,142 |
Losses and loss adjustment expenses, current accident year |  | 0 | [5] | 0 | [6] | 0 | [7]
Losses and loss adjustment expenses, prior accident years |  | (9,112) | [5] | (1,530) | [6] | (6,569) | [7]
Amortization of policy acquisition costs |  | 0 | [5] | 0 | [6] | 0 | [7]
Other underwriting expenses |  | 457 | [5] | (1,762) | [6] | (2,218) | [7]
Products expenses |  | 0 | [5] | 0 | [6] | 0 | [7]
Services and other expenses |  | (66,242) | [5] | (195,475) | [6] | (255,839) | [7]
Amortization of intangible assets |  | (98,244) | [1],[5] | (99,735) | [2],[6] | (102,971) | [3],[7]
Goodwill, Impairment Loss |  |  |  | (80,000) |  |  |
Segment profit (loss) |  | 106,990 | [5] | 115,244 | [6] | (25,455) | [7]
Underwriting [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Amortization of intangible assets |  | $ 37,076 | [8] | $ 38,533 | [8] | $ 41,200 |
[1] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $37.1 million for the year ended December 31, 2023.
[2] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $38.5 million for the year ended December 31, 2022.
[3] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $41.2 million for the year ended December 31, 2021.
[4] | Interest expense for the years ended December 31, 2023, 2022 and 2021 included intercompany interest expense of $26.5 million, $27.4 million and $25.8 million, respectively, which was eliminated in consolidation.
[5] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to the underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[6] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to the underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[7] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to the underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[8] | Amounts included in Underwriting reflect the intangible assets associated with the Company's underwriting segments, which are not allocated between the Insurance and Reinsurance segments.

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