Goodwill (Schedule Of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill, beginning Balance		$ 1,224.4
Fiscal Acquisitions	$ 12.1
Adjustments to acquisitions			$ (4.8)
Foreign Currency Translation and Other		(9.5)
Goodwill, ending balance	1,222.2	1,222.2
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		299.1
Fiscal Acquisitions	5.3
Foreign Currency Translation and Other		(5.8)
Goodwill, ending balance	298.6	298.6
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		265.6
Fiscal Acquisitions	2.3
Foreign Currency Translation and Other		(3.1)
Goodwill, ending balance	264.8	264.8
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		50.3
Fiscal Acquisitions	1.5
Goodwill, ending balance	51.8	51.8
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		104.2
Fiscal Acquisitions	1.3
Foreign Currency Translation and Other		(0.1)
Goodwill, ending balance	105.4	105.4
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		86.3
Fiscal Acquisitions	0.2
Foreign Currency Translation and Other		(0.2)
Goodwill, ending balance	86.3	86.3
MIG [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		73.4
Adjustments to acquisitions			0.3
Goodwill, ending balance	73.7	73.7
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		273.2
Fiscal Acquisitions	1.5
Adjustments to acquisitions			$ (5.1)
Foreign Currency Translation and Other		(0.2)
Goodwill, ending balance	269.4	269.4
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		57.0
Foreign Currency Translation and Other		(0.1)
Goodwill, ending balance	56.9	56.9
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance		15.3
Goodwill, ending balance	$ 15.3	$ 15.3