Receivables (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 38.7
Additions - charged to expense	6.1	$ 8.4
Transfer from (to) allowance for credit losses (see below)	(1.1)	9.5
Net recoveries, write-offs and other	0.3	3.2
Ending Balance	44.0	17.6
Net long-term customer receivables	118.3
Allowance for long term customer receivables [Roll Forward]
Beginning balance	47.1
Additions - charged to expense	6.4	13.7
Transfer from (to) allowance for doubtful accounts (see above)	1.1	(9.5)
Net recoveries, write-offs and other	(0.9)	(6.2)
Ending balance	$ 53.7	$ 49.1