Share-Based Compensation - Stock Options (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Options outstanding and exercisable under the Company's 1991 Equity and Performance Incentive Plan
Outstanding at January 1, 2018 | shares	2.3
Outstanding at January 1, 2018 | $ / shares	$ 29.68
Granted | shares	0.5
Granted | $ / shares	$ 17.54
Outstanding at March 31, 2018 | shares	2.8
Outstanding at March 31, 2018 | $ / shares	$ 27.28
Outstanding, weighted-average remaining contractual term	8 years
Outstanding, aggregate intrinsic value | $	$ 0.0
Options exercisable at March 31, 2018 | shares	1.6
Options exercisable at March 31, 2018 | $ / shares	$ 30.81
Options exercisable, weighted-average remaining contractual term	7 years
Options exercisable, aggregate intrinsic value | $	$ 0.0
Options vested and expected to vest(2) at March 31, 2018 | shares	2.6
Options vested and expected to vest(2) at March 31, 2018 | $ / shares	$ 27.47
Options vested and expected to vest, weighted-average remaining contractual term	8 years
Options vested and expected to vest, aggregate intrinsic value | $	$ 0.0