Stockholders' Equity - Stock Options (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
2015 Plan
Stock options with performance condition
Options granted with performance condition (in shares)		2.0	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)
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	$ 5.7	$ 11.2
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