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SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
 12 Months Ended
Dec. 31, 2025
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]  
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
WHITE MOUNTAINS INSURANCE GROUP, LTD.
SUMMARY OF INVESTMENTS—OTHER THAN
INVESTMENTS IN RELATED PARTIES
As of December 31, 2025

Millions
Cost or Amortized Cost
Carrying
Value		Fair
Value
Fixed maturity investments:   
U.S. Government and agency obligations$459.7 $460.3 $460.3 
Debt securities issued by corporations1,534.9 1,537.7 1,537.7 
Mortgage and asset-backed securities405.1 393.0 393.0 
Collateralized loan obligations 343.9 347.0 347.0 
Foreign government and agency obligations31.2 32.5 32.5 
Total fixed maturity investments2,774.8 2,770.5 2,770.5 
Short-term investments1,881.2 1,881.7 1,881.7 
Investment in MediaAlpha (1)
59.2 231.2 231.2 
Common equity securities:
Industrial, Miscellaneous and Other
353.7 452.3 452.3 
Exchange traded funds
30.6 30.7 30.7 
Total common equity securities384.3 483.0 483.0 
Other long-term investments (2)
2,378.8 2,958.5 2,958.5 
Total investments$7,478.3 $8,324.9 $8,324.9 
(1) Under GAAP, equity method eligible investments are considered related parties. White Mountains’s Investment in MediaAlpha is equity method eligible. See Note 17 — “Equity Method Eligible Investments.”
(2) Includes equity method eligible investments with a cost and carrying value of $1,727.3 and $2,375.1.