Stockholders' Equity and Stock-based Compensation (Options Outstanding and Vested) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of shares, outstanding	2,866,675
Weighted average exercise price per share, outstanding (in dollar per share)	$ 40.54
Weighted average remaining contractual life, outstanding	6 years
Number of shares, vested	2,099,200,000
Weighted average exercise price per share, vested (in dollar per share)	$ 28.39
Stock Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 34.02	$ 33.05	$ 18.03
Aggregate grant date fair value	$ 12.2	$ 12.1	$ 7.4
Intrinsic value of options exercised	$ 52.1	$ 71.7	$ 92.1
$1.90 - $1.90
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	$ 4.10
Exercise price range, upper limit (in dollar per share)	$ 13.50
Number of shares, outstanding	297,913
Weighted average exercise price per share, outstanding (in dollar per share)	$ 9.75
Weighted average remaining contractual life, outstanding	2 years 6 months
Number of shares, vested	297,913,000
Weighted average exercise price per share, vested (in dollar per share)	$ 9.75
$2.10 - $2.80
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	13.60
Exercise price range, upper limit (in dollar per share)	$ 25.17
Number of shares, outstanding	351,255
Weighted average exercise price per share, outstanding (in dollar per share)	$ 22.22
Weighted average remaining contractual life, outstanding	4 years 7 months 6 days
Number of shares, vested	347,391,000
Weighted average exercise price per share, vested (in dollar per share)	$ 22.19
$3.80 - $3.80
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	25.56
Exercise price range, upper limit (in dollar per share)	$ 25.56
Number of shares, outstanding	836,635
Weighted average exercise price per share, outstanding (in dollar per share)	$ 25.56
Weighted average remaining contractual life, outstanding	6 years 3 months 18 days
Number of shares, vested	764,382,000
Weighted average exercise price per share, vested (in dollar per share)	$ 25.56
$4.10 - $12.68
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	26.68
Exercise price range, upper limit (in dollar per share)	$ 34.97
Number of shares, outstanding	297,207
Weighted average exercise price per share, outstanding (in dollar per share)	$ 30.98
Weighted average remaining contractual life, outstanding	5 years
Number of shares, vested	287,277,000
Weighted average exercise price per share, vested (in dollar per share)	$ 30.96
$13.50 - $25.17
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	36.25
Exercise price range, upper limit (in dollar per share)	$ 40.68
Number of shares, outstanding	301,532
Weighted average exercise price per share, outstanding (in dollar per share)	$ 38.19
Weighted average remaining contractual life, outstanding	6 years 3 months 18 days
Number of shares, vested	244,236,000
Weighted average exercise price per share, vested (in dollar per share)	$ 38.17
$25.56 - $25.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	40.89
Exercise price range, upper limit (in dollar per share)	$ 79.51
Number of shares, outstanding	363,278
Weighted average exercise price per share, outstanding (in dollar per share)	$ 70.50
Weighted average remaining contractual life, outstanding	8 years 6 months
Number of shares, vested	113,388,000
Weighted average exercise price per share, vested (in dollar per share)	$ 61.81
$26.86 - $30.58
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	86.35
Exercise price range, upper limit (in dollar per share)	$ 87.26
Number of shares, outstanding	196,706
Weighted average exercise price per share, outstanding (in dollar per share)	$ 86.69
Weighted average remaining contractual life, outstanding	5 years 6 months
Number of shares, vested	2,770,000
Weighted average exercise price per share, vested (in dollar per share)	$ 87.26
$31.67 - $37.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	89.55
Exercise price range, upper limit (in dollar per share)	$ 89.55
Number of shares, outstanding	63,300
Weighted average exercise price per share, outstanding (in dollar per share)	$ 89.55
Weighted average remaining contractual life, outstanding	9 years 7 months 6 days
Number of shares, vested	499,000
Weighted average exercise price per share, vested (in dollar per share)	$ 89.55
$40.68 - $40.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	94.45
Exercise price range, upper limit (in dollar per share)	$ 94.45
Number of shares, outstanding	77,425
Weighted average exercise price per share, outstanding (in dollar per share)	$ 94.45
Weighted average remaining contractual life, outstanding	9 years
Number of shares, vested	10,458,000
Weighted average exercise price per share, vested (in dollar per share)	$ 94.45
$52.14 - $52.14
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	95.10
Exercise price range, upper limit (in dollar per share)	$ 95.10
Number of shares, outstanding	81,424
Weighted average exercise price per share, outstanding (in dollar per share)	$ 95.10
Weighted average remaining contractual life, outstanding	8 years 6 months
Number of shares, vested	30,886,000
Weighted average exercise price per share, vested (in dollar per share)	$ 95.10