Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Trade accounts receivable, allowance for doubtful accounts	$ 10.9	$ 12.8
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)	800,000,000	800,000,000
Issued (in shares)	574,128,911	571,803,838
Outstanding (in shares)	574,128,911	571,803,838

Amount of allowance for credit loss on accounts receivable, classified as current.

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