Revenue - Change in Contract Assets and Liabilities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Contract assets
Beginning accounts receivable, net of allowances	$ 194.8
Change in accounts receivable	10.4
Ending accounts receivable, net of allowances	205.2
Beginning unbilled contract revenue	54.5
Change in unbilled contract revenue	14.4
Ending unbilled contract revenue	$ 68.9
Change in accounts receivable (as a percentage)	5.30%
Change in unbilled contract revenue (as a percentage)	26.40%
Contract liabilities
Begining balance customer advances and billings in excess of contract revenue	$ 130.0
Change in customer advances and billings in excess of contract revenue	(0.5)
Ending balance customer advances and billings in excess of contract revenue	129.5
Beginning long-term deferred revenue	1.4
Change in long-term deferred revenue	(0.1)
Ending long-term deferred revenue	$ 1.3
Change in customer advances and billings in excess of contract revenue (as a percentage)	(0.40%)
Change in long-term deferred revenue (as a percentage)	(7.10%)