Other Financial Information - Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Financial Information [Abstract]
Interest income	$ 12.0	$ 8.5	$ 22.4	$ 16.4
Interest expense	(25.0)	(25.0)	(50.3)	(47.5)
Gain (loss) on investments, net	0.8	3.6	2.0	(1.8)
Other	(0.8)	1.3	(2.8)	(0.9)
Other expense, net	$ (13.0)	$ (11.6)	$ (28.7)	$ (33.8)