BUSINESS AND BASIS OF PRESENTATION (Impact of ASC 606 on Financials) (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Recently Issued Accounting Pronouncements
Revenues	$ 641.1				$ 643.1
Operating costs	228.4				235.7
Selling, general and administrative expenses	122.1				128.1
Depreciation and amortization	167.8				183.8
Provision for income taxes	20.5				5.4
Net income	22.1				23.3
Assets
Other current assets	31.6	$ 29.7				$ 29.7
Property and equipment, net	5,524.7	5,427.6				5,427.6
Other assets	170.4	175.6				175.6
Liabilities
Deferred revenue, current	171.6	162.9				162.9
Deferred revenue, non-current	1,085.6	1,076.3				1,076.3
Deferred income taxes, net	162.1	147.1				147.1
Stockholders' equity
Accumulated deficit	$ (343.9)	(366.0)				(366.0)
Accounting Standards Update 2014-09 [Member]
Recently Issued Accounting Pronouncements
Revenues		(0.3)	$ (0.4)	$ (0.4)	(0.4)	(1.5)	$ 20.5
Operating costs							18.8
Selling, general and administrative expenses		1.0	(0.3)	0.6	(0.2)	1.1	0.2
Depreciation and amortization		(0.1)	(0.2)	(0.3)	(0.3)	(0.9)	(0.7)
Provision for income taxes		(0.2)		(2.5)		(2.7)	0.8
Net income		(1.0)	$ 0.1	$ 1.8	$ 0.1	1.0	$ 1.4
As Previously Reported | Accounting Standards Update 2014-09 [Member]
Assets
Other current assets		22.6				22.6
Property and equipment, net		5,447.2				5,447.2
Other assets		170.0				170.0
Liabilities
Deferred revenue, current		164.4				164.4
Deferred revenue, non-current		1,096.8				1,096.8
Deferred income taxes, net		143.2				143.2
Stockholders' equity
Accumulated deficit		(377.2)				(377.2)
Effect of Adoption | Accounting Standards Update 2014-09 [Member]
Assets
Other current assets		7.1				7.1
Property and equipment, net		(19.6)				(19.6)
Other assets		5.6				5.6
Liabilities
Deferred revenue, current		(1.5)				(1.5)
Deferred revenue, non-current		(20.5)				(20.5)
Deferred income taxes, net		3.9				3.9
Stockholders' equity
Accumulated deficit		$ 11.2				$ 11.2