Statement of Cash Flows - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Accrued capital expenditures	$ 40.5		$ 40.5	$ 24.5	$ 41.8	$ 28.2
Capital lease obligations incurred				$ 201.2
Sanofi Collaboration Agreement, Immuno-oncology
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock, shares acquired	93,786	121,601	215,387
Cost of Treasury stock shares received	$ 38.1	$ 37.6	$ 75.8