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SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES | 12 Months Ended
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Dec. 31, 2021
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 At December 31, 2021
Millions |  | Cost |  | Carrying Value |  | Fair Value
Fixed maturity investments: |  |  |  |  |  |
U.S. Government and agency obligations |  | $ | 212.1 |  |  | $ | 211.5 |  |  | $ | 211.5 |
Debt securities issued by corporations |  | 993.3 |  |  | 992.9 |  |  | 992.9 |
Municipal obligations |  | 276.4 |  |  | 291.9 |  |  | 291.9 |
Mortgage and asset-backed securities |  | 277.2 |  |  | 277.6 |  |  | 277.6 |
Collateralized loan obligations |  | 136.5 |  |  | 135.0 |  |  | 135.0 |
Total fixed maturity investments |  | 1,895.5 |  |  | 1,908.9 |  |  | 1,908.9 |
Short-term investments |  | 465.9 |  |  | 465.9 |  |  | 465.9 |
Investment in MediaAlpha |  | — |  |  | 261.6 |  |  | 261.6 |
Common equity securities - Industrial, Miscellaneous, and Other |  | 236.3 |  |  | 251.1 |  |  | 251.1 |
Other long-term investments |  | 1,186.7 |  |  | 1,377.8 |  |  | 1,377.8 |
Total investments |  | $ | 3,784.4 |  |  | $ | 4,265.3 |  |  | $ | 4,265.3 |

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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 -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 15 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010 + Details
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