Share-based Compensation - Stock Options Activity Rollforward (Details) - Stock Options $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Number of Shares
Outstanding at beginning of period (shares) | shares	1,220
Granted (shares) | shares	190
Exercised (shares) | shares	(410)
Forfeited / Cancelled (shares) | shares	(210)
Outstanding at end of period (shares) | shares	790
Vested and expected to vest (shares) | shares	780
Exercisable at end of year (shares) | shares	350
Weighted-average Exercise Price
Outstanding at beginning of period (usd per share) | $ / shares	$ 32.64
Granted (usd per share) | $ / shares	48.98
Exercised (usd per share) | $ / shares	25.18
Forfeited / Cancelled (usd per share) | $ / shares	40.31
Outstanding at end of period (usd per share) | $ / shares	38.46
Vested and expected to vest at end of year (usd per share) | $ / shares	38.39
Exercisable at end of year (usd per share) | $ / shares	$ 45.22
Outstanding at end of year, aggregate intrinsic value | $	$ 22.3
Vested and expected to vest at end of year, aggregate intrinsic value | $	8.3
Exercisable at end of year, aggregate intrinsic value | $	$ 22.1
Outstanding at end of year, weighted average contractual term	5 years 110 days
Vested and expected to vest at end of year, weighted average contractual term	5 years 110 days
Exercisable at end of year, weighted average contractual term	4 years 110 days