SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT (Details 2) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Revenues (including realized gains and losses)	$ 678.5	$ 334.7	$ 403.6	$ 391.8	$ 405.6	$ 323.2	$ 393.5	$ 331.8	$ 1,808.6	$ 1,454.1	$ 1,361.6
Expenses	420.4	429.3	412.7	391.3	471.3	358.7	359.9	293.2	1,653.7	1,483.1	1,203.0
Pre-tax loss	258.1	(94.6)	(9.1)	0.5	(65.7)	(35.5)	33.6	38.6	154.9	(29.0)	158.6
Income tax (expense) benefit	1.5	1.6	2.2	(4.6)	26.2	4.7	(7.1)	(9.0)	0.7	14.8	(32.6)
Net income (loss) from continuing operations	259.6	(93.0)	(6.9)	(4.1)	(39.5)	(30.8)	26.5	29.6	155.6	(14.2)	126.0
Net income from discontinued operations, net of tax	7.3	14.2	3.5	73.8	82.1	63.9	61.1	51.5	80.6	260.2	99.9
Net income attributable to White Mountains’s common shareholders	267.9	(58.9)	4.3	84.3	69.9	51.3	95.5	95.5	297.6	312.2	321.6
Comprehensive income attributable to White Mountains’ common shareholders									197.2	210.6	241.8
Computation of net income (loss) available to common shareholders:
Net income attributable to White Mountains’s common shareholders	$ 267.9	$ (58.9)	$ 4.3	$ 84.3	$ 69.9	$ 51.3	$ 95.5	$ 95.5	297.6	312.2	321.6
White Mountains Insurance Group Ltd.
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Revenues (including realized gains and losses)									5.0	0.3	1.2
Expenses									59.9	32.3	39.0
Pre-tax loss									(54.9)	(32.0)	(37.8)
Income tax (expense) benefit									0.0	0.9	(0.1)
Net income (loss) from continuing operations									(54.9)	(31.1)	(37.9)
Net income from discontinued operations, net of tax									0.0	13.9	0.0
Equity in earnings (losses) from consolidated and unconsolidated affiliates									352.5	329.4	359.5
Net income attributable to White Mountains’s common shareholders									297.6	312.2	321.6
Other comprehensive income (loss), after-tax									(100.4)	(101.6)	(79.8)
Comprehensive income attributable to White Mountains’ common shareholders									197.2	210.6	241.8
Computation of net income (loss) available to common shareholders:
Net income attributable to White Mountains’s common shareholders									$ 297.6	$ 312.2	$ 321.6