Segment Information - Customer Revenue by Classes of Similar Products or Services (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Revenues	$ 495.2	$ 552.1	$ 1,449.4	$ 1,676.0
Services
Revenue from External Customer [Line Items]
Revenues	426.0	478.8	1,247.9	1,433.8
Technology
Revenue from External Customer [Line Items]
Revenues	69.2	73.3	201.5	242.2
Cloud & infrastructure services | Services
Revenue from External Customer [Line Items]
Revenues	294.1	325.4	865.0	967.6
Application services | Services
Revenue from External Customer [Line Items]
Revenues	91.1	93.5	258.6	279.1
Business process outsourcing services | Services
Revenue from External Customer [Line Items]
Revenues	$ 40.8	$ 59.9	$ 124.3	$ 187.1