SEGMENT REPORTING (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue from external customers	$ 649.4	$ 550.2	$ 1,946.4	$ 1,561.8
Segment Adjusted EBITDA	319.6	282.0	966.1	806.0
Total assets	9,241.5		9,241.5		$ 8,739.4
Capital expenditures	195.1	208.3	581.9	630.2
Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	210.3	179.6	606.3	531.2
Segment Adjusted EBITDA	164.6	137.6	479.8	416.8
Total assets	4,861.9		4,861.9		4,504.6
Capital expenditures	102.7	119.9	324.5	381.6
Transport [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	117.2	110.5	353.6	323.0
Segment Adjusted EBITDA	48.2	45.7	149.0	134.9
Total assets	1,306.6		1,306.6		1,230.0
Capital expenditures	40.5	40.2	106.0	111.1
Enterprise Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	138.8	121.7	422.4	350.8
Segment Adjusted EBITDA	50.5	46.6	157.0	126.9
Total assets	1,292.2		1,292.2		1,385.7
Capital expenditures	24.2	22.6	64.7	63.6
zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	59.6	53.6	177.9	157.3
Segment Adjusted EBITDA	29.4	28.7	90.3	82.6
Total assets	1,036.6		1,036.6		994.4
Capital expenditures	25.5	23.7	78.1	69.9
Allstream
Segment Reporting Information [Line Items]
Revenue from external customers	117.7	79.3	368.9	185.4
Segment Adjusted EBITDA	25.5	22.0	86.2	41.3
Total assets	467.0		467.0		406.2
Capital expenditures	2.2	1.9	8.6	4.0
Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	5.8	5.5	17.3	14.1
Segment Adjusted EBITDA	1.6	$ 1.4	4.0	$ 3.5
Total assets	33.2		33.2		33.2
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	(0.2)		(0.2)
Total assets	$ 244.0		$ 244.0		$ 185.3