Common Stock and Stock-Based Compensation Stockholders Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended					6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Apr. 29, 2021	Oct. 23, 2020
Share Repurchases [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 290.8	$ 36.8			$ 35.4
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			$ 77.1
Total Shares Repurchased Under Program	6,707,575					6,707,575
Total Shares Repurchased Under Program, Value	$ 172.9					$ 172.9
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%
Treasury Stock [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	10,500,000	1,300,000		0	1,900,000	11,800,000	1,900,000
Treasury Stock, Value, Acquired, Cost Method	$ 290.8	$ 36.8			$ 35.4	$ 327.6	$ 35.4
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	$ 68.3	$ 36.8	$ 67.8