Goodwill (Schedule Of Goodwill) (Detail) $ in Millions	3 Months Ended
	Sep. 30, 2015 USD ($)
Goodwill [Line Items]
Goodwill, beginning Balance	$ 1,224.4
Fiscal Acquisitions	(0.5)
Foreign Currency Translation and Other	(5.1)
Goodwill, ending balance	1,218.8
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	299.1
Foreign Currency Translation and Other	(3.2)
Goodwill, ending balance	295.9
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	265.6
Foreign Currency Translation and Other	(1.9)
Goodwill, ending balance	263.7
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	50.3
Goodwill, ending balance	50.3
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	104.2
Goodwill, ending balance	104.2
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	86.3
Goodwill, ending balance	86.3
MIG [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	73.4
Goodwill, ending balance	73.4
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	273.2
Fiscal Acquisitions	(0.5)
Goodwill, ending balance	272.7
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	57.0
Goodwill, ending balance	57.0
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	15.3
Goodwill, ending balance	$ 15.3