Inventories (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Inventories
Raw materials	$ 159.5	$ 189.7
Work-in-process	169.5	196.5
Finished goods	109.9	155.3
Demonstration units	38.5	48.3
Inventories	477.4	589.8
Inventory-in-transit	58.6	81.9
Write-down of demonstration units	$ 28.2	$ 32.7	$ 31.5