SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Assets
Other long-term investments	$ 1,488.0	$ 1,377.8
Total assets	7,389.3	7,000.7
Liabilities
Total liabilities	3,454.3	3,296.0
Total White Mountains’s common shareholders’ equity	3,746.9	3,548.1
Non-controlling interests	188.1	156.6
Total liabilities and equity	7,389.3	7,000.7
White Mountains Insurance Group Ltd.
Assets
Cash	0.1	0.6
Fixed maturity investments, at fair value	49.2	0.0
Common equity securities, at fair value	342.8	0.0
Other long-term investments	49.3	0.0
Short-term investments, at fair value	105.2	6.7
Other assets	75.3	3.0
Investments in consolidated subsidiaries	3,026.6	3,661.3
Total assets	3,648.5	3,671.6
Liabilities
Net Payable to subsidiary	(125.2)	104.9
Other liabilities	27.4	9.6
Total liabilities	(97.8)	114.5
Total White Mountains’s common shareholders’ equity	3,746.9	3,548.1
Non-controlling interests	(0.6)	9.0
Total liabilities and equity	$ 3,648.5	$ 3,671.6