Investments and Fair Value Measurements (Fair Value of Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	$ 5.3	$ 4.0
Equity securities and exchange-traded funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	21.9	17.3
Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	3.9	2.8
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	5.3	4.0
Cash equivalents, fair value disclosure	0.9	0.1
Investments, fair value disclosure	32.0	24.2
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and exchange-traded funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	21.9	17.3
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	3.9	2.8
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	0.0	0.0
Cash equivalents, fair value disclosure	0.0	0.0
Investments, fair value disclosure	0.0	0.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and exchange-traded funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	0.0	0.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	0.0	0.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	0.0	0.0
Cash equivalents, fair value disclosure	0.0	0.0
Investments, fair value disclosure	0.0	0.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and exchange-traded funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	0.0	0.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	0.0	0.0
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	5.3	4.0
Cash equivalents, fair value disclosure	0.9	0.1
Investments, fair value disclosure	32.0	24.2
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member] | Equity securities and exchange-traded funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	21.9	17.3
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member] | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 3.9	$ 2.8