Dispositions and Special Charges - Special Charges Liabilities (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
ETG – Lease liabilities and other costs | Lease Liabilities And Other Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 1.2
Charged to expense (income)	0.0
Paid or otherwise settled	(0.1)
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)	(0.1)
Paid or otherwise settled	(5.9)
Ending Balance	13.0
Total
Restructuring Reserve [Roll Forward]
Beginning Balance	20.2
Charged to expense (income)	(0.1)
Paid or otherwise settled	(6.0)
Ending Balance	$ 14.1