Common Stock and Stock-Based Compensation Stockholders Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 09, 2021	Apr. 29, 2021	Oct. 23, 2020
Share Repurchases [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 77.1	$ 290.8	$ 36.8		$ 89.9	$ 35.4
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 0.0						$ 0.0
Share-based Payment Arrangement, Cash Used to Settle Award					$ 4.9
2020-2021 Share Repurchase Program
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount											$ 250.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 77.1	$ 145.4	$ 182.2
Total Shares Repurchased Under Program	9,522,882						9,522,882
Total Shares Repurchased Under Program, Value	$ 250.0						$ 250.0
Special Share Repurchase Program
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount										$ 222.5
Stock Repurchase Program, Number of Shares Authorized to be Repurchased										8,100,000
Treasury Stock Acquired, Average Cost Per Share	$ 27.47
Treasury Stock Acquired, Per Share Discount										3.50%
2021-2022 Share Repurchase Program
Share Repurchases [Line Items]
Stock Repurchase Program, Authorized Amount									$ 250.0
Treasury Stock [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	2,815,307	10,500,000	1,300,000		4,500,000	1,900,000	14,600,000	6,300,000
Treasury Stock, Value, Acquired, Cost Method	$ 77.1	$ 290.8	$ 36.8		$ 89.9	$ 35.4	$ 404.7	$ 125.3
Treasury Stock [Member] | 2020-2021 Share Repurchase Program
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired		2,440,793	1,291,860	2,974,922
Treasury Stock, Value, Acquired, Cost Method	$ 77.1	$ 68.3	$ 36.8	$ 67.8