FAIR VALUE MEASUREMENTS - Fair Value of Other Temporary Investments and Cash (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 4,858.9	$ 4,395.1
Total Other Temporary Investments and Restricted Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost	238.7	236.9
Gross Unrealized Gains	28.0	26.9
Gross Unrealized Losses	(2.2)	(5.3)
Fair Value	264.5	258.5
Restricted Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost	39.1	43.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	39.1	43.1
Other Cash Deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost	12.2	13.9
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	12.2	13.9
Fixed Income Securities – Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost	173.3	167.2
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(2.2)	(5.3)
Fair Value	171.1	161.9
Equity Securities – Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost	14.1	12.7
Gross Unrealized Gains	28.0	26.9
Gross Unrealized Losses	0.0	0.0
Fair Value	$ 42.1	$ 39.6

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).

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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).

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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).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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