Income Taxes (Reconciliations of Actual Income Tax Provision and Tax Computed by Applying United States Federal Rate to Earnings Before Income Taxes) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Expected benefit at the statutory rate	$ (0.1)	$ (0.3)	$ (4.3)	$ (35.6)
Non-deductible stock-based compensation	10.0	(5.1)	17.4	42.1
State income taxes benefit, net of federal benefit	0.1		(0.5)	(4.5)
Transaction costs not deductible for tax purposes	0.5	0.1	0.5	0.4
Foreign tax rate differential	0.4	(0.3)	0.3	0.8
Other, net	0.2	1.3	0.4	1.9
Total provision for income taxes	11.1	(4.3)	13.8	5.1
Zayo Group, LLC [Member]
Total provision for income taxes	$ 10.3	$ (4.2)	$ 12.2	$ 4.4