COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Millions, $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 30, 2019 CAD ($) action stockholder	Jun. 30, 2019 CAD ($) action	Jun. 30, 2019 USD ($)	Jun. 30, 2019 CAD ($) action	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2019 USD ($) action
Commitment And Contingencies [Line Items]
Lease expense					$ 238.7	$ 156.4	$ 68.8
Expense related to right-of way, pole attachment and other fees for access					43.8	$ 43.4	$ 65.1
Purchase commitments								$ 471.1
Outstanding letters of credit								$ 8.5
Number of stockholders, filed complaints | stockholder	3
Commitment for telecom services 2 year period [Member]
Commitment And Contingencies [Line Items]
Other commitments		$ 90.0	$ 68.8	$ 127.0	$ 97.0
Other commitments period				2 years	2 years
Commitment for telecom services 3 year period [Member]
Commitment And Contingencies [Line Items]
Other commitments		$ 25.3	$ 19.3	$ 40.0	$ 30.6
Other commitments period				3 years	3 years
District Court of Delaware [Member]
Commitment And Contingencies [Line Items]
Number of actions pending | action	4	4		4				4
District Court of Colorado [Member]
Commitment And Contingencies [Line Items]
Number of actions pending | action	1	1		1				1
District Court of Boulder County [Member]
Commitment And Contingencies [Line Items]
Number of actions pending | action	1	1		1				1
Zayo Canada, Inc | Credit Letter Agreement [Member]
Commitment And Contingencies [Line Items]
Outstanding letters of credit	$ 3.5	$ 3.5		$ 3.5				$ 2.6
Unsecured credit agreement	$ 5.0	$ 5.0		$ 5.0				$ 3.8