Revenue recognition, Contract liabilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Contract with Customer, Liability [Abstract]
Deferral of revenue	$ 29.3
Recognition of revenue included in beginning of year contract liability	(29.1)
Contract liability	73.1
Accounting Standards Update 2014-09 [Member]
Contract with Customer, Liability [Abstract]
Contract liability	72.9
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Contract with Customer, Liability [Abstract]
Contract liability	42.4
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | CIADM [Member] | Accounting Standards Update 2014-09 [Member]
Contract with Customer, Liability [Abstract]
Contract liability	42.4
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Contract with Customer, Liability [Abstract]
Contract liability	$ 30.5