Fair Value of Financial Instruments (Schedule of Summarized Financial Information of Equity Method Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summarized Financial Information of Equity Method Investments [Line Items]
Current assets	$ 144.5	$ 137.3
Long-term assets	1,359.9	1,352.1
Total assets	1,504.4	1,489.4
Current liabilities	34.9	31.3
Long-term liabilities	978.6	966.1
Total liabilities	1,013.5	997.4
Revenue	152.4	145.8	$ 114.5
Net income	$ 82.8	$ 72.4	$ 64.5