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FAIR VALUE MEASUREMENTS - Fair Value of Other Temporary Investments and Cash (Details) - USD ($) $ in Millions | Mar. 31, 2025 | Dec. 31, 2024
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fair Value | $ 4,309.3 | $ 4,395.1
Total Other Temporary Investments and Restricted Cash |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cost | 224.3 | 236.9
Gross Unrealized Gains | 21.6 | 26.9
Gross Unrealized Losses | (3.9) | (5.3)
Fair Value | 242.0 | 258.5
Restricted Cash |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cost | 35.2 | 43.1
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.0 | 0.0
Fair Value | 35.2 | 43.1
Other Cash Deposits |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cost | 13.9 | 13.9
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.0 | 0.0
Fair Value | 13.9 | 13.9
Fixed Income Securities – Mutual Funds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cost | 164.2 | 167.2
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (3.9) | (5.3)
Fair Value | 160.3 | 161.9
Equity Securities – Mutual Funds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cost | 11.0 | 12.7
Gross Unrealized Gains | 21.6 | 26.9
Gross Unrealized Losses | 0.0 | 0.0
Fair Value | $ 32.6 | $ 39.6

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
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- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
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