Goodwill (Schedule Of Goodwill) (Details) $ in Millions	9 Months Ended
	Mar. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill, beginning Balance	$ 1,214.5
Adjustments to Fiscal 2016 Acquisitions	(5.3)
Fiscal 2017 Acquisitions	625.2
Foreign Currency Translation and Other	(11.8)
Goodwill, ending balance	1,822.6
Dark Fiber [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	295.1
Reallocation among reporting units	(295.1)
Fiber Solutions [Member]
Goodwill [Line Items]
Reallocation among reporting units	544.8
Adjustments to Fiscal 2016 Acquisitions	1.7
Fiscal 2017 Acquisitions	34.7
Foreign Currency Translation and Other	(8.9)
Goodwill, ending balance	572.3
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	258.3
Reallocation among reporting units	(104.0)
Adjustments to Fiscal 2016 Acquisitions	(2.7)
Fiscal 2017 Acquisitions	25.4
Foreign Currency Translation and Other	(2.7)
Goodwill, ending balance	174.3
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	51.3
Reallocation among reporting units	0.7
Fiscal 2017 Acquisitions	75.1
Foreign Currency Translation and Other	(0.1)
Goodwill, ending balance	127.0
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	104.3
Reallocation among reporting units	(59.8)
Adjustments to Fiscal 2016 Acquisitions	(0.5)
Fiscal 2017 Acquisitions	52.1
Foreign Currency Translation and Other	(0.1)
Goodwill, ending balance	96.0
IP [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	87.5
Reallocation among reporting units	(87.5)
MIG [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	73.6
Reallocation among reporting units	(73.6)
EPIC [Member]
Goodwill [Line Items]
Reallocation among reporting units	89.5
Fiscal 2017 Acquisitions	90.2
Foreign Currency Translation and Other	(0.2)
Goodwill, ending balance	179.5
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	268.8
Reallocation among reporting units	(15.0)
Adjustments to Fiscal 2016 Acquisitions	(3.7)
Foreign Currency Translation and Other	0.2
Goodwill, ending balance	250.3
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	60.0
Adjustments to Fiscal 2016 Acquisitions	(0.1)
Fiscal 2017 Acquisitions	2.2
Goodwill, ending balance	62.1
Allstream
Goodwill [Line Items]
Fiscal 2017 Acquisitions	345.5
Goodwill, ending balance	345.5
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	15.6
Goodwill, ending balance	$ 15.6