Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets - current	$ 32.7		$ 32.7		$ 29.7
Contract assets - long-term	24.5		24.5		22.2
Deferred revenue - current	(288.3)		(288.3)		(294.4)
Deferred revenue - long-term	(147.0)		(147.0)		(157.2)
Deposit liabilities principally included in current deferred revenue	32.6		32.6		$ 21.2
Revenue recognized that was previously included in deferred revenue	$ 85.7	$ 86.3	$ 190.6	$ 190.9