SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION

12 Months Ended

Dec. 31, 2024

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]

SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION

WHITE MOUNTAINS INSURANCE GROUP, LTD.

SUPPLEMENTARY INSURANCE INFORMATION

	Column A	Column B		Column C		Column D		Column E		Column F		Column G		Column H		Column  I		Column J		Column K
	Millions	Deferred Acquisition Costs		Future Policy Benefits, Losses, Claims and Loss Expenses		Unearned Premiums		Other Policy Claims and Benefits Payable		Premiums Earned		Net Investment Income		Benefits, Claims, Losses and Settlement Expenses		Amortization of Deferred Acquisition Costs		Other Operating Expenses		Premiums Written
Years ended:
December 31, 2024
	Ark/WM Outrigger	$	165.2	$	2,127.5	$	853.3	$	—	$	1,587.8	$	90.7	$	855.8	$	294.1	$	136.1	$	1,679.1
	HG Global	86.6		—		297.3		—		31.7		32.2		—		8.2		.2		56.0
	Bamboo Captive	10.2		17.8		31.5		—		39.4		1.4		20.6		14.1		—		50.0
	Bamboo CRV	5.8		12.1		29.0		—		32.7		.4		12.1		12.1		—		61.7
December 31, 2023
	Ark/WM Outrigger	145.3		1,605.1		743.6		—		1,409.7		61.4		726.8		273.1		113.6		1,520.9
	HG Global	40.1		—		325.8		—		31.2		31.7		—		8.6		.4		58.6
December 31, 2022
	Ark/WM Outrigger	127.2		1,296.5		623.2		—		1,043.4		16.3		536.4		238.3		78.7		1,195.2
	HG Global	36.0		—		298.3		—		33.3		21.5		—		11.2		.4		65.1

Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.