Sales - Contract liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Deferred revenue - current	$ 288.1	$ 211.4
Deferred revenue - noncurrent	92.6	86.7
Total contract liabilities	380.7	298.1
Additional contract liabilities	380.7	$ 298.1
Contract liabilities, revenue recognized	119.0
2018 Acquisitions
Disaggregation of Revenue [Line Items]
Total contract liabilities	35.0
Additional contract liabilities	$ 35.0