Revenue - Change in Contract Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contract assets
Accounts receivable, net of allowances	$ 196.4	$ 196.4
Change in accounts receivable	(1.6)	(25.5)	$ 32.8	$ (35.8)
Accounts receivable, net of allowances	194.8	194.8	196.4
Unbilled contract revenue	43.0
Change in unbilled contract revenue	11.5
Unbilled contract revenue	$ 54.5	54.5
Change in accounts receivable (as a percentage)	0.80%
Change in unbilled contract revenue (as a percentage)	(26.70%)
Contract liabilities
Customer advances and billings in excess of contract revenue	$ 101.8	109.6
Change in customer advances and billings in excess of contract revenue	28.2	4.9	15.9	$ 5.0
Customer advances and billings in excess of contract revenue	130.0	130.0	$ 109.6
Long-term deferred revenue	1.7
Change in long-term deferred revenue	(0.3)
Long-term deferred revenue	$ 1.4	$ 1.4
Change in customer advances and billings in excess of contract revenue (as a percentage)	(27.70%)
Change in long-term deferred revenue (as a percentage)	17.60%