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SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES | 12 Months Ended
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Dec. 31, 2023
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, 2023
Millions |  | Cost |  | Carrying Value |  | Fair Value
Fixed maturity investments: |  |  |  |  |  |
U.S. Government and agency obligations |  | $ | 209.0 |  |  | $ | 204.9 |  |  | $ | 204.9 |
Debt securities issued by corporations |  | 1,085.9 |  |  | 1,045.0 |  |  | 1,045.0 |
Municipal obligations |  | 275.1 |  |  | 260.9 |  |  | 260.9 |
Mortgage and asset-backed securities |  | 417.2 |  |  | 389.4 |  |  | 389.4 |
Collateralized loan obligations |  | 211.2 |  |  | 209.1 |  |  | 209.1 |
Total fixed maturity investments |  | 2,198.4 |  |  | 2,109.3 |  |  | 2,109.3 |
Short-term investments |  | 1,487.0 |  |  | 1,487.9 |  |  | 1,487.9 |
Investment in MediaAlpha |  | 59.2 |  |  | 254.9 |  |  | 254.9 |
Common equity securities: |  |  |  |  |  |
Common equity securities - Industrial, Miscellaneous, and Other |  | 370.2 |  |  | 400.6 |  |  | 400.6 |
Common equity securities - Exchange traded funds |  | 113.3 |  |  | 137.8 |  |  | 137.8 |
Total common equity securities |  | 483.5 |  |  | 538.4 |  |  | 538.4 |
Other long-term investments |  | 1,655.7 |  |  | 1,998.2 |  |  | 1,998.2 |
Total investments |  | $ | 5,883.8 |  |  | $ | 6,388.7 |  |  | $ | 6,388.7 |

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- Definition The entire disclosure of information about investment held by insurance company, excluding investment in related party. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 15 -Publisher SEC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480032/946-320-S99-7 + Details
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