Share Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Nov. 29, 2018	May 25, 2017
Equity, Class of Treasury Stock [Line Items]
Value of shares repurchased	$ 175,000,000	$ 25,000,000
5/25/2017 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount (in usd)				$ 200,000,000.0
Shares repurchased	2.7	0.3
Value of shares repurchased	$ 175,000,000	$ 25,000,000
Treasury stock acquired, average cost per share (in usd per share)	$ 64.94	$ 79.75
Amount remaining of authorized amount for repurchase under the share repurchase program (in usd)	$ 0
11/29/2018 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount (in usd)			$ 300,000,000
Shares repurchased	0.0