Goodwill (Schedule Of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015
Goodwill [Line Items]
Goodwill, beginning Balance		$ 1,224.4
Fiscal Acquisitions	$ 12.7
Adjustments to acquisitions			$ (5.0)
Foreign Currency Translation and Other		(12.5)
Goodwill, ending balance	1,219.6	1,219.6
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		299.1
Fiscal Acquisitions	1.4
Foreign Currency Translation and Other		(7.8)
Goodwill, ending balance	292.7	292.7
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		265.6
Fiscal Acquisitions	4.9
Foreign Currency Translation and Other		(4.4)
Goodwill, ending balance	266.1	266.1
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		50.3
Fiscal Acquisitions	1.0
Goodwill, ending balance	51.3	51.3
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		104.2
Fiscal Acquisitions	0.4
Goodwill, ending balance	104.6	104.6
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		86.3
Fiscal Acquisitions	1.5
Goodwill, ending balance	87.8	87.8
MIG [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		73.4
Adjustments to acquisitions			0.2
Goodwill, ending balance	73.6	73.6
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		273.2
Fiscal Acquisitions	3.5
Adjustments to acquisitions			(5.3)
Foreign Currency Translation and Other		(0.3)
Goodwill, ending balance	271.1	271.1
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		57.0
Goodwill, ending balance	57.0	57.0
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		15.3
Adjustments to acquisitions			$ 0.1
Goodwill, ending balance	$ 15.4	$ 15.4