Segment Information - Customer Revenue by Classes of Similar Products or Services (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from External Customer [Line Items]
Revenues	$ 695.8	$ 708.4
Services
Revenue from External Customer [Line Items]
Revenues	612.1	568.5
Technology
Revenue from External Customer [Line Items]
Revenues	83.7	139.9
Cloud & infrastructure services | Services
Revenue from External Customer [Line Items]
Revenues	361.2	318.4
Application services | Services
Revenue from External Customer [Line Items]
Revenues	189.1	192.9
Business process outsourcing services | Services
Revenue from External Customer [Line Items]
Revenues	$ 61.8	$ 57.2