Common Stock and Stock-Based Compensation Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount						$ 350.0
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						13,700,000
Treasury Stock, Shares, Acquired						866,715
Treasury Stock, Value, Acquired, Cost Method		$ 35.4			$ 44.0	$ 19.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 89.9	$ 89.9	$ 125.3	$ 186.1	287.0	331.0	$ 287.0
Total Shares Repurchased Under Program	12,954,794
Total Shares Repurchased Under Program, Value	$ 260.1
Share-based Payment Arrangement, Accelerated Cost							$ 70.0
Additional Paid-in Capital [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired							2,600,000
Treasury Stock, Value, Acquired, Cost Method					$ 0.0	$ 70.0
Treasury Stock [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	0	1,850,000	2,933,474	5,171,489	2,133,116	3,500,000
Treasury Stock, Value, Acquired, Cost Method	$ 0.0	$ 35.4	$ 60.8	$ 100.9	$ 44.0	$ 89.0