SEGMENT REPORTING (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue from external customers	$ 650.6	$ 647.2	$ 639.1	$ 641.1	$ 657.3	$ 649.0	$ 653.1	$ 643.1	$ 2,578.0	$ 2,602.5	$ 2,220.3
Segment Adjusted EBITDA									1,283.1	1,288.3	1,118.2
Total assets	9,334.6				9,209.9				9,334.6	9,209.9
Capital expenditures									786.9	789.9	835.5
Reportable Segments [Member] | Zayo Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									1,896.7	1,808.8	1,621.1
Segment Adjusted EBITDA									1,087.5	1,026.0	904.6
Total assets	7,677.5				7,406.7				7,677.5	7,406.7
Capital expenditures									667.8	667.5	723.5
Reportable Segments [Member] | zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									269.9	290.7	263.3
Segment Adjusted EBITDA									125.0	142.3	125.2
Total assets	1,152.3				1,188.5				1,152.3	1,188.5
Capital expenditures									99.8	108.8	103.5
Reportable Segments [Member] | Allstream [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									381.7	479.9	314.3
Segment Adjusted EBITDA									64.8	115.0	83.3
Total assets	376.9				465.5				376.9	465.5
Capital expenditures									19.3	13.6	8.5
Reportable Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									29.7	23.1	21.6
Segment Adjusted EBITDA									5.8	5.0	$ 5.1
Total assets	35.1				33.4				35.1	33.4
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 92.8				$ 115.8				$ 92.8	$ 115.8