Other Financial Information - Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Financial Information [Abstract]
Interest income	$ 18.9	$ 14.7	$ 49.8	$ 37.1
Interest expense	(25.8)	(25.3)	(77.7)	(75.6)
(Loss) gain on investments, net	(1.9)	4.7	(1.8)	6.7
Other	0.7	0.8	(1.4)	(2.0)
Other expense, net	$ (8.1)	$ (5.1)	$ (31.1)	$ (33.8)