Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Mar. 16, 2020	Mar. 31, 2020	Dec. 31, 2019	Feb. 21, 2019
Markel Ventures [Member] \| Industrial products [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		$ 20.2	$ 33.5
Anthony Belisle v. Markel CATCo Investment Management Ltd and Markel Corp. [Member]
Loss Contingencies [Line Items]
Asserted claims				$ 66.0
Lansing Building Products, LLC [Member]
Loss Contingencies [Line Items]
Total purchase consideration	$ 546.7
Lodgepine Fund Limited [Member]
Loss Contingencies [Line Items]
Other commitment		$ 100.0