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Subsequent Event	6 Months Ended
	Jun. 30, 2012
Note 15. Subsequent Event [Abstract]
Subsequent Events [Text Block]	Note 15. Subsequent Event In July 2012, White Mountains invested approximately $600 million in HG Global Ltd. ("HG Global"), which will reinsure municipal bond insurance risks written by Build America Mutual Assurance Company ("BAM") through a wholly-owned subsidiary, HG Re Ltd. White Mountains owns 98% of HG Global's preferred equity and 89% of its common equity. White Mountains expects to syndicate approximately $110 million of its investment to interested investors in the near future to broaden the support for BAM.

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- Definition

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

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