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Transactions with Related Persons	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Transactions with Related Persons	Transactions with Related PersonsDuring 2017, the Company repurchased shares from Franklin Mutual Advisers, a beneficial owner of the Company. On July 13, 2017, the Company repurchased 235,000 White Mountains common shares for $850.00 per share, the market price at the time the agreement was reached.

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- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-URI http://asc.fasb.org/topic&trid=2122745

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