Common Stock and Stock-Based Compensation Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Oct. 23, 2020
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount						$ 350.0	$ 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	$ 89.9		$ 35.4		$ 100.9	$ 44.0	$ 19.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 0.0	$ 89.9	$ 89.9	$ 125.3	186.1	287.0	331.0	$ 186.1
Total Shares Repurchased Under Program	17,421,690
Total Shares Repurchased Under Program, Value	$ 350.0
Share-based Payment Arrangement, Cash Used to Settle Award	$ 4.9
Share-based Payment Arrangement, Accelerated Cost								$ 70.0
Subsequent Event [Member]
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount									$ 250.0
Additional Paid-in Capital [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired								2,600,000
Treasury Stock, Value, Acquired, Cost Method					$ 0.0	$ 0.0	$ 70.0
Treasury Stock [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	4,466,896	0	1,850,000	2,933,474	5,171,489	2,133,116	3,500,000
Treasury Stock, Value, Acquired, Cost Method	$ 89.9	$ 0.0	$ 35.4	$ 60.8	$ 100.9	$ 44.0	$ 89.0