CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Earned insurance premiums	$ 1,076.7	$ 664.2	$ 22.8
Net investment income	124.4	82.5	131.0
Net realized and unrealized investment gains (losses)	(98.5)	134.2	30.8
Net realized and unrealized investment gains (losses) from investment in MediaAlpha	(93.0)	(380.3)	686.0
Commission revenues	11.5	9.6	8.3
Other revenues	136.8	104.2	16.7
Total revenues	1,157.9	614.4	895.6
Expenses:
Loss and loss adjustment expenses	536.4	314.8
Insurance acquisition expenses	250.6	186.3	7.0
Cost of sales	98.6	69.3	11.3
General and administrative expenses	376.2	292.5	207.9
Amortization of other intangible assets	5.2	4.6	1.6
Interest expense	40.3	20.5	7.4
Total expenses	1,307.3	888.0	235.2
Pre-tax income (loss) from continuing operations	(149.4)	(273.6)	660.4
Income tax (expense) benefit	(41.4)	(44.4)	14.8
Net income (loss) from continuing operations	(190.8)	(318.0)	675.2
Net income (loss) from discontinued operations, net of tax - NSM Group	16.4	(22.6)	(9.5)
Net income (loss)	712.4	(321.9)	663.4
Net (income) loss attributable to non-controlling interests	80.4	46.5	45.3
Net income (loss) attributable to White Mountains’s common shareholders	792.8	(275.4)	708.7
Sirius Group
Expenses:
Net gain (loss) from sale of discontinued operations, net of tax	0.0	18.7	(2.3)
NSM
Expenses:
Net income (loss) from discontinued operations, net of tax - NSM Group	16.4	(22.6)	(9.5)
Net gain (loss) from sale of discontinued operations, net of tax	886.8	0.0	0.0
HG Global-BAM
Revenues:
Earned insurance premiums	33.3	26.9	22.8
Net investment income	21.5	17.5	19.5
Net realized and unrealized investment gains (losses)	(105.8)	(22.9)	23.7
Net realized and unrealized investment gains (losses) from investment in MediaAlpha	0.0	0.0	0.0
Commission revenues	0.0	0.0	0.0
Other revenues	4.6	1.5	2.5
Total revenues	(46.4)	23.0	68.5
Expenses:
Loss and loss adjustment expenses	0.0	0.0
Insurance acquisition expenses	11.2	8.3	7.0
Cost of sales	0.0	0.0	0.0
General and administrative expenses	69.1	57.1	56.8
Amortization of other intangible assets	0.0	0.0	0.0
Interest expense	8.3	0.0	0.0
Total expenses	88.6	65.4	63.8
Pre-tax income (loss) from continuing operations	(135.0)	(42.4)	4.7
Ark
Revenues:
Earned insurance premiums	1,043.4	637.3	0.0
Net investment income	16.3	2.9	0.0
Net realized and unrealized investment gains (losses)	(55.2)	16.5	0.0
Net realized and unrealized investment gains (losses) from investment in MediaAlpha	0.0	0.0
Commission revenues	0.0	0.0
Other revenues	5.0	11.8	0.0
Total revenues	1,009.5	668.5	0.0
Expenses:
Loss and loss adjustment expenses	536.4	314.8	0.0
Insurance acquisition expenses	239.4	178.0	0.0
Cost of sales	0.0	0.0
General and administrative expenses	123.5	115.5	0.0
Amortization of other intangible assets	0.0	0.0
Interest expense	15.1	7.3	0.0
Total expenses	914.4	615.6	0.0
Pre-tax income (loss) from continuing operations	95.1	52.9
Kudu
Revenues:
Earned insurance premiums	0.0	0.0	0.0
Net investment income	54.4	43.9	29.5
Net realized and unrealized investment gains (losses)	64.1	89.9	15.9
Net realized and unrealized investment gains (losses) from investment in MediaAlpha	0.0	0.0	0.0
Commission revenues	0.0	0.0	0.0
Other revenues	0.0	0.2	0.3
Total revenues	118.5	134.0	45.7
Expenses:
Loss and loss adjustment expenses	0.0
Insurance acquisition expenses	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0
General and administrative expenses	14.4	14.5	11.8
Amortization of other intangible assets	0.3	0.3	0.3
Interest expense	15.0	11.7	6.0
Total expenses	29.7	26.5	18.1
Pre-tax income (loss) from continuing operations	88.8	107.5	27.6
Other Operations
Revenues:
Earned insurance premiums	0.0	0.0	0.0
Net investment income	32.2	18.2	82.0
Net realized and unrealized investment gains (losses)	(1.6)	50.7	(8.8)
Net realized and unrealized investment gains (losses) from investment in MediaAlpha	(93.0)	(380.3)	686.0
Commission revenues	11.5	9.6	8.3
Other revenues	127.2	90.7	13.9
Total revenues	76.3	(211.1)	781.4
Expenses:
Loss and loss adjustment expenses	0.0	0.0
Insurance acquisition expenses	0.0	0.0	0.0
Cost of sales	98.6	69.3	11.3
General and administrative expenses	169.2	105.4	139.3
Amortization of other intangible assets	4.9	4.3	1.3
Interest expense	1.9	1.5	1.4
Total expenses	274.6	180.5	153.3
Pre-tax income (loss) from continuing operations	$ (198.3)	$ (391.6)	$ 628.1