Segment Reporting (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue from external customers	$ 643.5	$ 504.9
Segment Adjusted EBITDA	316.6	260.6
Total assets	8,862.4		$ 8,739.4
Capital expenditures	193.4	208.3
Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	195.5	174.1
Segment Adjusted EBITDA	154.2	138.3
Total assets	4,517.9		4,504.6
Capital expenditures	107.3	130.8
Transport [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	119.1	106.1
Segment Adjusted EBITDA	51.6	44.6
Total assets	1,256.5		1,230.0
Capital expenditures	33.7	33.5
Enterprise Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	137.7	114.4
Segment Adjusted EBITDA	49.5	40.6
Total assets	1,394.6		1,385.7
Capital expenditures	21.0	20.9
zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	58.4	51.2
Segment Adjusted EBITDA	29.4	26.3
Total assets	1,005.5		994.4
Capital expenditures	27.9	22.9
Allstream
Segment Reporting Information [Line Items]
Revenue from external customers	127.7	54.5
Segment Adjusted EBITDA	30.8	9.7
Total assets	424.3		406.2
Capital expenditures	3.5	0.2
Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	5.1	4.6
Segment Adjusted EBITDA	1.1	$ 1.1
Total assets	32.2		33.2
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 231.4		$ 185.3

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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