SEGMENT REPORTING (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue from external customers	$ 653.5	$ 506.7	$ 1,297.0	$ 1,011.6
Segment Adjusted EBITDA	329.9	263.4	646.5	524.0
Total assets	8,935.9		8,935.9		$ 8,739.4
Capital expenditures	193.4	213.6	386.8	421.9
Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	200.5	177.5	396.0	351.6
Segment Adjusted EBITDA	161.0	141.0	315.2	279.2
Total assets	4,701.7		4,701.7		4,504.6
Capital expenditures	114.5	130.9	221.8	261.7
Transport [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	117.3	106.4	236.4	212.5
Segment Adjusted EBITDA	49.2	44.6	100.8	89.2
Total assets	1,257.6		1,257.6		1,230.0
Capital expenditures	31.8	37.4	65.5	70.9
Enterprise Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	145.9	114.7	283.6	229.1
Segment Adjusted EBITDA	57.0	39.7	106.5	80.3
Total assets	1,293.2		1,293.2		1,385.7
Capital expenditures	19.5	20.1	40.5	41.0
zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	59.9	52.5	118.3	103.7
Segment Adjusted EBITDA	31.5	27.6	60.9	53.9
Total assets	1,007.1		1,007.1		994.4
Capital expenditures	24.7	23.3	52.6	46.2
Allstream
Segment Reporting Information [Line Items]
Revenue from external customers	123.5	51.6	251.2	106.1
Segment Adjusted EBITDA	29.9	9.6	60.7	19.3
Total assets	487.1		487.1		406.2
Capital expenditures	2.9	1.9	6.4	2.1
Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	6.4	4.0	11.5	8.6
Segment Adjusted EBITDA	1.3	$ 0.9	2.4	$ 2.1
Total assets	32.3		32.3		33.2
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 156.9		$ 156.9		$ 185.3