Investments - Investments Held at Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016
Investments Held at Cost
Payments made to acquire investments held at cost			$ 25.1	$ 7.6
Impairment charges		$ 46.5	46.5
Privately-held Companies
Investments Held at Cost
Payments made to acquire investments held at cost		25.1	25.1
Privately-held Companies | Other Non-current assets
Investments Held at Cost
Cost method investments, after adjustments for impairment		151.8	151.8
Preferred stock in privately-held company | Forecast
Investments Held at Cost
Payments made to acquire investments held at cost	$ 30.0
Cost Method Investment One | Privately-held Companies
Investments Held at Cost
Cost method investments, after adjustments for impairment		$ 53.5	53.5
Impairment charges			$ 46.5