Other expenses - Other Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Income and Expenses [Abstract]
Severance and employee benefits	$ 3.6	$ 2.3	$ 0.3
Non-cash share based compensation	0.0	0.0	0.1
Acquisition related costs	19.8	19.7	3.1
Transitioned employees restructuring expense	3.0	4.3	1.2
Digital Transformation Office	8.6	3.6	0.0
Other	1.2	0.5	0.0
Total other	36.2	$ 30.4	$ 4.7
Restructuring liability	1.1
Reorganization receivable	$ 0.7