Contract with customer, asset and liability (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract with Customer, Asset, before Allowance for Credit Loss	$ 372.8	$ 534.7	$ 523.5
change in contract asset	(161.9)	11.2
Contract with Customer, Liability	(469.6)	(514.6)	(527.7)
change in contract liability	45.0	13.1
Contract with Customer, Liability, Revenue Recognized	118.2	139.0
Contracts with Customers, Net Contract Asset (Liability)	(96.8)	20.1	$ (4.2)
change in net contract asset	$ (116.9)	$ 24.3