Income Taxes - Composition of Income (Loss) Before Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 1,801.0	$ 1,754.4
Less accumulated depreciation	$ (909.3)	(878.6)	(834.1)
Property and equipment, net	$ 930.2	922.4	920.3
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross		27.6	25.1
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, gross		567.2	557.7
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross		1,025.1	994.5
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 181.1	$ 177.1

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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