Common Stock and Stock-Based Compensation Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Nov. 16, 2018	Dec. 31, 2017
Share Repurchases [Line Items]
Shares_repurchased_settled_in_subsequent_month	$ 4.0
Stock Repurchase Program, Authorized Amount	350.0			$ 500.0
Accelerated Share Repurchase Program, Authorized Amount			$ 350.0
Shares repurchased	(19.0)	$ (50.0)
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 331.0
Treasury Stock [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	3,473,887	1,519,503
Shares repurchased	$ 89.0	$ 50.0
Additional Paid-in Capital [Member]
Share Repurchases [Line Items]
Treasury Stock, Shares, Acquired	2,607,172
Shares repurchased	$ 70.0