Cost reduction actions - Additional Information (Detail) $ in Millions	3 Months Ended							12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) Employee	Dec. 31, 2015 USD ($) Employee
Restructuring Cost and Reserve [Line Items]
Estimated future restructuring charges					$ 300.0				$ 300.0
Restructuring charges	$ 13.1	$ 31.9	$ 10.2	$ 26.9	$ 48.5	$ 17.4	$ 52.6	$ 82.1	118.5
Severance costs								62.6	78.8
Asset impairments and other expenses related to the cost reduction effort								19.5	39.7
Asset impairment charges									20.2
Cost of revenue | Services
Restructuring Cost and Reserve [Line Items]
Restructuring charges								42.4	52.3
Cost of revenue | Technology
Restructuring Cost and Reserve [Line Items]
Restructuring charges									0.3
Selling, general and administrative expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges								38.0	53.5
Research and development expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges								1.7	12.4
Other expenses related to the cost reduction effort
Restructuring Cost and Reserve [Line Items]
Restructuring charges								13.3	19.5
Net asset sales and write-offs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								0.7
Idle leased facilities and contract amendment and termination
Restructuring Cost and Reserve [Line Items]
Restructuring charges								5.5
United States
Restructuring Cost and Reserve [Line Items]
Severance costs								$ 7.0	$ 27.9
Number of employees | Employee								351	700
Non-US
Restructuring Cost and Reserve [Line Items]
Severance costs								$ 55.6	$ 50.9
Number of employees | Employee								1,048	782