Share-Based Compensation (Unrecognized Compensation Cost, Nonvested Awards) (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense not yet recognized (in millions)	$ 77.9
Weighted-average recognition period (in years)	2 years 2 months 12 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration