Segment Information - Summary of Operations by Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 757.6	$ 688.3	$ 2,207.2	$ 2,064.1
Operating income (loss)	70.9	55.8	200.8	211.6
Services
Segment Reporting Information [Line Items]
Revenue	654.1	605.6	1,919.6	1,760.8
Operating income (loss)	36.1	18.6	90.5	54.3
Technology
Segment Reporting Information [Line Items]
Revenue	103.5	82.7	287.6	303.3
Operating income (loss)	34.9	34.5	119.4	154.7
Intersegment
Segment Reporting Information [Line Items]
Revenue	(2.3)	(4.3)	(6.8)	(18.3)
Intersegment | Services
Segment Reporting Information [Line Items]
Revenue	0.0	0.0	0.0	0.0
Intersegment | Technology
Segment Reporting Information [Line Items]
Revenue	2.3	4.3	6.8	18.3
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	71.0	53.1	209.9	209.0
Operating Segments | Services
Segment Reporting Information [Line Items]
Revenue	654.1	605.6	1,919.6	1,760.8
Operating Segments | Technology
Segment Reporting Information [Line Items]
Revenue	105.8	87.0	294.4	321.6
Corporate
Segment Reporting Information [Line Items]
Revenue	(2.3)	(4.3)	(6.8)	(18.3)
Operating income (loss)	$ (0.1)	$ 2.7	$ (9.1)	$ 2.6