Common Stock and Treasury Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions								12 Months Ended
	Nov. 13, 2017	May 06, 2016	May 03, 2016	May 02, 2016	Feb. 24, 2016	Feb. 22, 2016	Feb. 19, 2016	Dec. 31, 2018	Dec. 31, 2015	Dec. 31, 2017
Class of Stock [Line Items]
Shares of treasury stock into a rabbi trust (in shares)								10,646,382	291,919
Average cost (in dollars per share)								$ 50.62
Average cost, commission (in dollars per share)								$ 0.02
Shares of treasury stock transferred (in shares)									17,000,000
Treasury stock, held in rabbi trust (in shares)								0		253,145
Public Stock Offering
Class of Stock [Line Items]
Number of shares issued in transaction (in shares)				10,500,000			6,500,000
Price per share (in dollars per share)				$ 67.00			$ 58.50
Consideration received		$ 795.6			$ 430.4
Over-Allotment Option
Class of Stock [Line Items]
Number of shares issued in transaction (in shares)			1,575,000			975,000
Rice Merger Agreement
Class of Stock [Line Items]
Number of shares issued in business combination (in shares)	91,000,000