Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Contract assets
Beginning accounts receivable, net of allowances	$ 222.7	$ 222.7
Change in accounts receivable	17.9	(15.4)	$ 16.2
Ending accounts receivable, net of allowances	207.3	$ 207.3
Change in accounts receivable (as a percentage)		6.90%
Beginning unbilled contract revenue	37.0	$ 43.5
Change in unbilled contract revenue	6.4	(5.8)	(4.9)
Ending unbilled contract revenue	37.7	$ 37.7
Change in unbilled contract revenue (as a percentage)		13.30%
Contract liabilities
Beginning customer advances and billings in excess of contract revenue	110.2	$ 100.3
Change in customer advances and billings in excess of contract revenue	13.0	14.4	$ 4.4
Ending customer advances and billings in excess of contract revenue	114.7	$ 114.7
Change in customer advances and billings in excess of contract revenue (as a percentage)		(14.40%)
Beginning long-term deferred revenue		$ 2.6
Change in long-term deferred revenue		0.1
Ending long-term deferred revenue	$ 2.7	$ 2.7
Change in long-term deferred revenue (as a percentage)		(3.80%)