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Products, Services and Other Revenues Products, Services and Other Revenues (Receivables Related To Contracts With Customers) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Receivables [Line Items]
Trade and other receivables	$ 3,486,395	$ 2,983,173
Contracts with customers [Member]
Receivables [Line Items]
Trade and other receivables	$ 616,400	$ 624,100

X

- Definition

[Line Items] for Other Revenues [Table]

+ References

No definition available.

+ Details

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Namespace Prefix:	mkl_
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X

- Definition

Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-2

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Period Type:	instant

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Balance Type:
Period Type: