Segment Information - Additional Information (Detail) $ in Millions		3 Months Ended								12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment customer	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Revenue		$ 760.9	$ 688.3	$ 667.4	$ 708.4	$ 744.8	$ 666.3	$ 666.2	$ 664.5	$ 2,825.0	$ 2,741.8		$ 2,820.7
Number of business segments | segment										2
Operating profit (loss)										$ 284.1	97.1	[1]	129.2	[1]
Number of customers accounted for more than 10% of revenue | customer										0
Various Agencies Of U.S. Government
Segment Reporting Information [Line Items]
Revenue										$ 574.0	571.0		564.0
Other Technology | Segment Reconciling Items
Segment Reporting Information [Line Items]
Operating profit (loss)										4.2	6.3		0.7
Technology
Segment Reporting Information [Line Items]
Revenue										438.7	413.6		414.4
Operating profit (loss)										$ 237.8	$ 170.6		$ 161.5
Technology | Software License Extensions and Renewals
Segment Reporting Information [Line Items]
Revenue	$ 53.0				$ 53.0

[1] Amounts were changed to conform to the current-year presentation. See Note 2.