Business Acquisitions - Narrative (Details) - USD ($)		9 Months Ended
	Feb. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Feb. 28, 2018	Jan. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired		$ 1,118,000,000	$ 110,300,000
Goodwill		$ 1,766,400,000				$ 1,089,000,000
Line of Credit | Term Loan Agreement
Business Acquisition [Line Items]
Line of credit, maximum borrowing capacity	$ 500,000,000				$ 500,000,000
Senior Notes | Notes 2028 Term
Business Acquisition [Line Items]
Interest rate, stated percentage	3.50%	3.50%		3.50%
Principal amount of debt	$ 450,000,000			$ 450,000,000
Aclara
Business Acquisition [Line Items]
Consideration transferred to acquire business	1,100,000,000
Acquisition of businesses, net of cash acquired	1,116,300,000
Goodwill	$ 685,100,000
Sales of acquiree since acquisition		$ 429,700,000
Operating income of acquiree since acquisition		12,800,000
Other acquisition
Business Acquisition [Line Items]
Amount received to settle net working capital adjustment		$ 1,700,000