Contract assets and deferred revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets - current	$ 44.3	$ 38.4
Contract assets - long-term	20.7	21.6
Deferred revenue - current	(257.1)	(246.4)
Deferred revenue - long-term	(137.9)	(147.0)
Revenue recognized that was included in deferred revenue at the beginning of the period	$ 236.1	$ 270.1