Goodwill (Schedule Of Goodwill) (Details) $ in Millions	6 Months Ended
	Dec. 31, 2016 USD ($)
Goodwill [Line Items]
Goodwill, beginning Balance	$ 1,214.5
Adjustments to acquisitions	(3.6)
Foreign Currency Translation and Other	(14.0)
Goodwill, ending balance	1,196.9
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	295.1
Adjustments to acquisitions	1.7
Foreign Currency Translation and Other	(9.6)
Goodwill, ending balance	287.2
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	258.3
Adjustments to acquisitions	(2.7)
Foreign Currency Translation and Other	(3.3)
Goodwill, ending balance	252.3
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	51.3
Foreign Currency Translation and Other	(0.1)
Goodwill, ending balance	51.2
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	104.3
Adjustments to acquisitions	(0.5)
Foreign Currency Translation and Other	(0.2)
Goodwill, ending balance	103.6
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	87.5
Foreign Currency Translation and Other	(0.4)
Goodwill, ending balance	87.1
MIG [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	73.6
Goodwill, ending balance	73.6
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	268.8
Adjustments to acquisitions	(2.0)
Foreign Currency Translation and Other	(0.2)
Goodwill, ending balance	266.6
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	60.0
Adjustments to acquisitions	(0.1)
Goodwill, ending balance	59.9
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	15.6
Foreign Currency Translation and Other	(0.2)
Goodwill, ending balance	$ 15.4