Dispositions and Special Charges - Special Charges Liabilities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Corporate – Lease liabilities and other costs | Lease Liabilities And Other Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 1.2
Charged to expense (income)	0.1
Paid or otherwise settled	(0.2)
Ending Balance	1.1
NATG – Lease liabilities and other exit costs | Lease Liabilities and Other Exit Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	19.0
Charged to expense (income)	2.5
Paid or otherwise settled	(14.8)
Ending Balance	6.7
Total
Restructuring Reserve [Roll Forward]
Beginning Balance	20.2
Charged to expense (income)	2.6
Paid or otherwise settled	(15.0)
Ending Balance	$ 7.8