Revenue - Change in Contract Assets and Liabilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Contract assets
Accounts receivable, net of allowances, beginning	$ 191.6
Change in accounts receivable	9.2
Accounts receivable, net of allowances, ending	200.8
Unbilled contract revenue, beginning	86.1
Change in unbilled contract revenue	(6.7)
Unbilled contract revenue, ending	$ 79.4
Change in accounts receivable (as a percentage)	4.80%
Change in unbilled contract revenue (as a percentage)	(7.80%)
Contract liabilities
Customer advances and billings in excess of contract revenue, beginning	$ 127.7
Change in customer advances and billings in excess of contract revenue	(8.8)
Customer advances and billings in excess of contract revenue, ending	118.9
Long term deferred revenue, beginning	0.8
Change in long-term deferred revenue	1.1
Long-term deferred revenue, ending	$ 1.9
Change in customer advances and billings in excess of contract revenue (as a percentage)	(6.90%)
Change in long-term deferred revenue (as a percentage)	137.50%