Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Trade accounts receivable, allowance for doubtful accounts	$ 12.8	$ 11.9
Preferred stock:
Par value (in dollars per share)	$ 0.01	$ 0.01
Authorized (in shares)	5,000,000	5,000,000
Issued (in shares)	0	0
Outstanding (in shares)	0	0
Common stock:
Par value (in dollars per share)	$ 0.01	$ 0.01
Authorized (in shares)	400,000,000	400,000,000
Issued (in shares)	285,901,919	287,591,536
Outstanding (in shares)	285,901,919	287,591,536

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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