Segment Information - Customer Revenue by Classes of Similar Products or Services (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue from External Customer [Line Items]
Revenues	$ 666.2	$ 748.9	$ 1,330.7	$ 1,415.7
Services
Revenue from External Customer [Line Items]
Revenues	574.8	613.8	1,160.1	1,208.9
Technology
Revenue from External Customer [Line Items]
Revenues	91.4	135.1	170.6	206.8
Cloud & infrastructure services | Services
Revenue from External Customer [Line Items]
Revenues	326.9	340.0	662.2	675.9
Application services | Services
Revenue from External Customer [Line Items]
Revenues	196.4	220.4	397.9	431.0
Business process outsourcing services | Services
Revenue from External Customer [Line Items]
Revenues	$ 51.5	$ 53.4	$ 100.0	$ 102.0