Supplemental Cash Flow Information - Supplemental Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental cash flow information
Cash (paid) for interest, net of amount capitalized	$ (441.5)	$ (413.7)	$ (411.9)
Cash received (paid) for income taxes, net	(16.3)	5.2	39.7
Accounts payable related to construction costs	65.9	169.2	170.1
Receivable related to corporate-owned life insurance proceeds	7.7	0.0	0.0
Bostco
Supplemental cash flow information
Portion of Bostco real estate holdings sale financed with note receivable	$ 0.0	$ 7.0	$ 0.0