Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Summary of unaudited consolidated pro forma results of operations
Revenues	$ 5,658.6	$ 5,621.8	$ 17,365.7	$ 16,432.4
Income from continuing operations	130.1	95.4	372.7	288.9
Net income	$ 130.2	$ 95.5	$ 373.0	$ 288.6
Income from continuing operations per diluted common share (in dollars per share)	$ 1.53	$ 1.11	$ 4.37	$ 3.36
Net income per diluted common share (in dollars per share)	$ 1.53	$ 1.11	$ 4.37	$ 3.36

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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