Stockholders' Equity - Stock Options (Details) - USD ($) shares in Millions, $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
2015 Plan
Stock options with performance condition
Options granted with performance condition (in shares)	1.9	1.6
ASU 2016-09
Recently Issued Accounting Standards
Cumulative effect on retained earnings, Net of tax	$ (5.8)
Cumulative effect on retained earnings, Tax	(3.2)
ASU 2016-09 \| 2015 Plan
Recently Issued Accounting Standards
Cumulative effect on retained earnings, Net of tax	(0.4)
Cumulative effect on retained earnings, Tax	$ (0.2)
Performance Shares \| 2015 Plan
Stock options with performance condition
Options granted with performance condition (in shares)	0.9
Aggregate grant date fair value	$ 53.9
Allocated Share-based Compensation Expense	$ 5.5
Performance Shares \| 2015 Plan \| Minimum
Stock options with performance condition
Vesting period (in years)	1 year
Performance Shares \| 2015 Plan \| Maximum
Stock options with performance condition
Vesting period (in years)	3 years

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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Amount of the cumulative effect on retained earnings net of related income tax effect.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 2
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Gross number of share options (or share units) granted during the period.

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Represents the total grant date fair value of option granted during the reporting period.

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