Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables, Net, Current [Abstract]
Accounts receivable, allowances	$ 8.3	$ 8.4	$ 9.8
Property and equipment, accumulated depreciation	$ 909.3	$ 878.6	$ 834.1
Common stock, shares authorized	5,000,000,000	5,000,000,000
Common stock, shares issued	365,702,757	365,643,911
Common stock, shares outstanding	365,702,757	365,643,911

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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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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