Revenue (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Contract assets
Beginning accounts receivable, net of allowances	$ 222.7	$ 222.7
Change in accounts receivable	(20.6)	(18.3)	$ 5.8
Ending accounts receivable, net of allowances	204.4	204.4
Beginning unbilled contract revenue	37.0	43.5
Change in unbilled contract revenue	0.0	(2.3)	(6.2)
Ending unbilled contract revenue	41.2	$ 41.2
Change in accounts receivable (as a percentage)		8.20%
Change in unbilled contract revenue (as a percentage)		5.30%
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	8.8	8.6	$ (3.4)
Ending customer advances and billings in excess of contract revenue	108.9	108.9
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%)
Change in customer advances and billings in excess of contract revenue (as a percentage)		(8.60%)