Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowances for doubtful accounts	$ 27.6	$ 28.9	$ 53.5	$ 50.1
Preferred stock, par value (in dollars per shares)	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares authorized	500,000.0	500,000.0	500,000
Preferred stock, shares issued	0	0	0
Treasury stock, shares	2,700,000	2,300,000
Common Class A
Common stock, par value (in dollars per share)	$ 0.025	$ 0.025	$ 0.025
Common stock, shares authorized	80,000,000	80,000,000	80,000,000
Common stock, shares issued	40,300,000	40,000,000	40,000,000
Treasury stock, shares	2,200,000	1,800,000	2,800,000
Common Class B
Common stock, par value (in dollars per share)	$ 0.025	$ 0.025	$ 0.025
Common stock, shares authorized	80,000,000	80,000,000	80,000,000
Common stock, shares issued	13,500,000	13,800,000	15,000,000
Treasury stock, shares	0	0	800,000
Common Class C
Common stock, par value (in dollars per share)	$ 0.025	$ 0.025	$ 0.025
Common stock, shares authorized	20,000,000	20,000,000	20,000,000
Common stock, shares issued	500,000	500,000	500,000
Treasury stock, shares	500,000	500,000	500,000

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.4)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
-Section 45
-Paragraph 1
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