Employee Benefit Plans (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Number of Shares
Balance at beginning of period (in shares)	2.4
Exercised (in shares)	(0.2)
Expired/canceled (in shares)	(0.6)
Balance at end of period (in shares)	1.6
Weighted Average Exercise Price per Share
Balance at beginning of period (in dollars per share) | $ / shares	$ 29.20
Exercised (in dollars per share) | $ / shares	21.39
Expired/canceled (in dollars per share) | $ / shares	30.63
Balance at end of period (in dollars per share) | $ / shares	$ 29.83
Weighted average remaining contractual term at end of period	1 year 9 months 18 days
Aggregate intrinsic value at end of period | $	$ 8.0
Vested or expected-to-vest options at end of period (in shares)	1.6
Vested or expected-to-vest options, weighted average exercise price at end of period (in dollars per share) | $ / shares	$ 29.83
Vested and expected-to-vest options, weighted average remaining contractual term at end of period	1 year 9 months 18 days
Vested or expected-to-vest options, aggregate intrinsic value at end of period | $	$ 8.0
Exercisable options at end of period (in shares)	1.5
Exercisable options, weighted average exercise price at end of period (in dollars per share) | $ / shares	$ 30.82
Exercisable options, weighted average remaining contractual term at end of period	1 year 6 months
Exercisable options, aggregate intrinsic value at end of period | $	$ 6.6
Equity incentive plan 2015 [Member]
Share-Based Compensation Plans
Number of shares available for future issuance	11.6
Employee stock purchase plan 2008 [Member]
Share-Based Compensation Plans
Number of shares available for future issuance	3.4