Goodwill (Schedule Of Goodwill) (Details) $ in Millions	3 Months Ended
	Sep. 30, 2016 USD ($)
Goodwill [Line Items]
Goodwill, beginning Balance	$ 1,214.5
Foreign Currency Translation and Other	(3.9)
Goodwill, ending balance	1,210.6
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	295.1
Foreign Currency Translation and Other	(2.6)
Goodwill, ending balance	292.5
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	258.3
Foreign Currency Translation and Other	(1.2)
Goodwill, ending balance	257.1
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	51.3
Goodwill, ending balance	51.3
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	104.3
Goodwill, ending balance	104.3
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	87.5
Goodwill, ending balance	87.5
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
Goodwill, ending balance	268.8
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	60.0
Goodwill, ending balance	60.0
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	15.6
Foreign Currency Translation and Other	(0.1)
Goodwill, ending balance	$ 15.5