Employee Benefits - Schedule of actuarial gains and losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefit Plans, Accumulated Net Gains Losses [Roll Forward]
Cumulative actuarial (losses) gains at beginning of year	$ (3.4)	$ (6.4)	$ (10.8)
Actuarial gains (losses) recognized during the period, net of tax	2.2	1.8	3.3
Amortization of net loss	0.1	0.1	0.3
Curtailments, settlements and terminations	0.0	0.0	2.1
Foreign exchange movement	(0.2)	1.1	(1.3)
Cumulative actuarial losses at end of year	(1.3)	(3.4)	(6.4)
Actuarial gains (losses) recognized during the period, tax	$ 0.8	$ 0.6	$ (1.1)