INCOME TAXES (Reconciliation of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Expected expense/(benefit) at the statutory rate	$ 9.6	$ (3.9)	$ 24.4	$ (8.2)
Non-deductible stock-based compensation		5.2	4.0	22.6
Excess tax benefit on stock-based compensation	(13.1)		(16.7)
State income taxes benefit, net of federal benefit	0.6	(0.2)	2.1	(0.7)
Transaction costs not deductible for tax purposes	1.5	0.6	1.8	1.1
Change in tax rates			(1.7)
Foreign tax rate differential	(1.8)	0.5	(2.1)	0.8
Foreign entities with valuation allowance	(2.0)		(8.7)
Other, net	5.8	5.6	4.3	6.0
Provision/(benefit) for income taxes	0.6	7.8	7.4	21.6
Zayo Group, LLC [Member]
Provision/(benefit) for income taxes	$ 0.7	$ 8.0	$ 9.2	$ 20.0