Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets - current	$ 38.3		$ 38.3		$ 29.7
Contract assets - long-term	22.4		22.4		22.2
Deferred revenue - current	(236.0)		(236.0)		(294.4)
Deferred revenue - long-term	(142.4)		(142.4)		(157.2)
Deposit liabilities principally included in current deferred revenue	16.8		16.8		$ 21.2
Revenue recognized that was previously included in deferred revenue	$ 46.0	$ 64.6	$ 236.6	$ 255.5