Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Allowance for trade accounts receivables	$ 12.4	$ 12.9
Class A Common Stock
Capital stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares issued (in shares)	36.6	36.6
Treasury stock, common stock (in shares)	1.3	1.7
Class B Common Stock
Capital stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares issued (in shares)	3.5	3.5

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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