SEGMENT REPORTING (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenue from external customers	$ 641.1	$ 643.1
Segment Adjusted EBITDA	319.4	316.4
Total assets	9,314.9		$ 9,209.9
Capital expenditures	182.5	193.4
Reportable Segments [Member] \| Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	220.9	198.4
Segment Adjusted EBITDA	178.4	159.7
Total assets	4,991.0		4,937.3
Capital expenditures	99.1	107.3
Reportable Segments [Member] \| Transport [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	168.4	168.0
Segment Adjusted EBITDA	57.1	60.3
Total assets	1,878.0		1,870.9
Capital expenditures	40.4	44.3
Reportable Segments [Member] \| Enterprise Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	82.6	85.4
Segment Adjusted EBITDA	34.0	33.4
Total assets	755.9		754.6
Capital expenditures	13.2	10.4
Reportable Segments [Member] \| zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	59.0	58.4
Segment Adjusted EBITDA	28.0	28.6
Total assets	1,038.4		1,032.4
Capital expenditures	25.2	27.9
Reportable Segments [Member] \| Allstream [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	105.0	127.7
Segment Adjusted EBITDA	20.8	33.2
Total assets	427.3		465.5
Capital expenditures	4.6	3.5
Reportable Segments [Member] \| Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	5.2	5.2
Segment Adjusted EBITDA	1.1	1.3
Total assets	32.4		33.4
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA		$ (0.1)
Total assets	$ 191.9		$ 115.8

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
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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