Goodwill (Schedule Of Goodwill) (Details) $ in Millions	3 Months Ended
	Sep. 30, 2017 USD ($)
Goodwill [Line Items]
Goodwill, beginning Balance	$ 1,840.2
Adjustments to Fiscal Acquisitions	(1.2)
Foreign Currency Translation and Other	5.1
Goodwill, ending balance	1,844.1
Fiber Solutions [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	633.9
Adjustments to Fiscal Acquisitions	0.2
Foreign Currency Translation and Other	2.5
Goodwill, ending balance	636.6
Waves [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	247.4
Foreign Currency Translation and Other	1.3
Goodwill, ending balance	248.7
Sonet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	52.0
Goodwill, ending balance	52.0
Ethernet [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	359.5
Foreign Currency Translation and Other	0.2
Goodwill, ending balance	359.7
EPIC [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	89.5
Foreign Currency Translation and Other	0.2
Goodwill, ending balance	89.7
zColo [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	256.3
Adjustments to Fiscal Acquisitions	(3.1)
Foreign Currency Translation and Other	0.9
Goodwill, ending balance	254.1
Cloud [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	69.5
Goodwill, ending balance	69.5
Allstream
Goodwill [Line Items]
Goodwill, beginning Balance	116.5
Goodwill, ending balance	116.5
Other [Member]
Goodwill [Line Items]
Goodwill, beginning Balance	15.6
Adjustments to Fiscal Acquisitions	1.7
Goodwill, ending balance	$ 17.3