Cost-reduction actions - Statement of Income Classifications (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	$ 9.3	$ 54.9	$ 23.2
Cost of revenue | Services
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	4.9	19.1	(2.5)
Cost of revenue | Technology
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	0.7	7.6	7.6
Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	6.9	24.7	11.1
Research and development
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	0.5	0.6	3.0
Other (expenses), net
Restructuring Cost and Reserve [Line Items]
Cost-reduction charges and other costs	$ (3.7)	$ 2.9	$ 4.0