Segment Information - Customer Revenue by Classes of Similar Products or Services (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue from External Customer [Line Items]
Revenues	$ 515.4	$ 554.5
Services
Revenue from External Customer [Line Items]
Revenues	425.9	474.0
Technology
Revenue from External Customer [Line Items]
Revenues	89.5	80.5
Cloud & infrastructure services | Services
Revenue from External Customer [Line Items]
Revenues	295.2	321.7
Application services | Services
Revenue from External Customer [Line Items]
Revenues	85.1	90.5
Business process outsourcing services | Services
Revenue from External Customer [Line Items]
Revenues	$ 45.6	$ 61.8