SEGMENT REPORTING (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenue from external customers	$ 638.6	$ 641.1
Segment Adjusted EBITDA	314.8	319.4
Total assets	9,881.8		$ 9,334.6
Capital expenditures	217.1	182.5
Reportable Segments [Member] | Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	483.2	461.6
Segment Adjusted EBITDA	277.5	266.2
Total assets	7,992.4		7,677.5
Capital expenditures	194.8	149.2
Reportable Segments [Member] | zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	63.7	69.3
Segment Adjusted EBITDA	26.6	31.3
Total assets	1,312.2		1,152.3
Capital expenditures	18.1	28.7
Reportable Segments [Member] | Allstream [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	86.6	105.0
Segment Adjusted EBITDA	9.3	20.8
Total assets	388.6		376.9
Capital expenditures	4.2	4.6
Reportable Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	5.1	5.2
Segment Adjusted EBITDA	1.4	$ 1.1
Total assets	33.1		35.1
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 155.5		$ 92.8