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Fair Value Measurements (Financial Instruments Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Trading Securities at Fair Value $ 101.3 $ 84.5
Investments, Fair Value Disclosure 8.6  
Fair Value, Measurements, Recurring [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, Fair Value Disclosure 111.7 96.0
Total Assets at Fair Value 111.7 96.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 1 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, Fair Value Disclosure 111.7 96.0
Total Assets at Fair Value 111.7 96.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 2 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, Fair Value Disclosure 0.0 0.0
Total Assets at Fair Value 0.0 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 3 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, Fair Value Disclosure 0.0 0.0
Total Assets at Fair Value 0.0 0.0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 10.2 11.3
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 1 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 10.2 11.3
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 2 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 0.0 0.0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 3 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 0.0 0.0
Mutual Fund [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Trading Securities at Fair Value 101.3 84.5
Mutual Fund [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 1 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Trading Securities at Fair Value 101.3 84.5
Mutual Fund [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 2 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Trading Securities at Fair Value 0.0 0.0
Mutual Fund [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 3 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Trading Securities at Fair Value 0.0  
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 0.2 0.2
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 1 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 0.2 0.2
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 2 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities 0.0 0.0
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, level 3 [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Marketable Securities $ 0.0 $ 0.0