CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Revenues:
Earned insurance and reinsurance premiums	$ 536.8		$ 491.1		$ 1,545.3		$ 1,433.5
Net investment income	37.6		42.8		119.8		138.1
Net realized and unrealized investment gains (losses)	72.7		2.9		123.2		36.4
Other revenue	50.3		(35.0)		81.0		(28.3)
Total revenues	697.4		501.8		1,869.3		1,579.7
Expenses:
Loss and loss adjustment expenses	308.1		280.2		821.7		920.4
Insurance and reinsurance acquisition expenses	107.6		107.0		326.2		296.6
Other underwriting expenses	76.6		64.3		228.4		203.9
General and administrative expenses	58.7		36.2		146.3		120.4
Interest expense on debt	11.3		12.8		33.1		38.8
Total expenses	562.3		500.5		1,555.7		1,580.1
Pre-tax income (loss) from continuing operations	135.1		1.3		313.6		(0.4)
Income tax (expense) benefit	(47.8)		0.6		(85.3)		(0.8)
Net income (loss) from continuing operations	87.3		1.9		228.3		(1.2)
Gain (loss) on sale of discontinued operation, net of tax	(91.0)		(18.2)		(91.0)		(18.2)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(15.8)		(12.0)		(24.5)		(7.8)
Income (loss) before equity in earnings of unconsolidated affiliates	(19.5)		(28.3)		112.8		(27.2)
Equity in earnings of unconsolidated affiliates	7.7		1.5		24.4		16.1
Net income (loss)	(11.8)		(26.8)		137.2		(11.1)
Net (Income) Loss Attributable to Noncontrolling Interest	30.9		11.0		2.0		(21.2)
Net income (loss) attributable to White Mountains' common shareholders	19.1		(15.8)		139.2		(32.3)
Comprehensive income (loss), net of tax:
Change in equity in net unrealized losses from investments in unconsolidated affiliates	32.3		55.1		59.3		77.2
Other Comprehensive Income (Loss) Foreign Currency Translation and Other	39.6		(81.8)		33.3		(25.3)
Comprehensive income	91.0		(42.5)		231.8		19.6
Comprehensive income attributable to noncontrolling interests	0.4		0		0.4		0
Comprehensive income attributable to White Mountains’ common shareholders	91.4		(42.5)		232.2		19.6
Basic income (loss) per share
Continuing operations (in dollars per share)	$ 19.11		$ 1.81		$ 36.96		$ (0.80)
Discontinued operations (in dollars per share)	$ (16.21)		$ (3.81)		$ (16.77)		$ (3.26)
Total consolidated operations (in dollars per share)	$ 2.90		$ (2.00)		$ 20.19		$ (4.06)
Diluted income (loss) per share
Continuing operations (in dollars per share)	$ 19.11		$ 1.81		$ 36.96		$ (0.80)
Discontinued operations (in dollars per share)	$ (16.21)		$ (3.81)		$ (16.77)		$ (3.26)
Total consolidated operations (in dollars per share)	$ 2.90		$ (2.00)		$ 20.19		$ (4.06)
Dividends declared per White Mountains' common share (in dollars per share)	$ 0.00		$ 0.00		$ 1.00		$ 1.00
Segment, Discontinued Operations [Member]
Revenues:
Earned insurance and reinsurance premiums	(0.4)		233.3		10.0		701.9
Net investment income	0		3.8		0		11.8
Net realized and unrealized investment gains (losses)	0		(6.4)		0		1.4
Other revenue	0		17.5		0		54.0
Total revenues	(0.4)		248.2		10.0		769.1
Expenses:
Loss and loss adjustment expenses	27.7		177.4		48.4		512.3
Insurance and reinsurance acquisition expenses	(0.8)		51.4		(1.3)		154.1
Other underwriting expenses	(1.1)		35.0		1.1		83.9
General and administrative expenses	0		1.7		0		37.5
Total expenses	25.8		265.5		48.2		787.8
Gain (loss) on sale of discontinued operation, net of tax	(91.0)		(18.2)		(91.0)		18.2
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(15.8)		(12.0)		(24.5)		(7.8)
Net income (loss) attributable to White Mountains' common shareholders	$ (105.3)	[1]	$ (29.9)	[1]	$ (114.0)	[1]	$ (25.8)	[1]

[1] (2) Net loss attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed loss for the three and nine months ended September 30, 2012 and 2011.