BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Impact of ASC 606 on Financials) (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
Recently Issued Accounting Pronouncements
Revenues	$ 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
Operating costs	238.6	226.3	222.0	228.4	239.3	234.9	232.0	235.7	915.3	941.9	801.7
Selling, general and administrative expenses	133.3	128.1	125.5	122.1	122.9	117.7	122.2	128.1	509.0	490.9	436.4
Depreciation and amortization	157.5	161.2	146.9	167.8	176.1	190.9	195.7	183.8	633.4	746.5	606.2
Provision for income taxes	(35.7)	18.0	22.5	20.5	(23.4)	21.0	20.4	5.4	25.3	23.4	19.2
Net income	63.0	$ 34.7	$ 30.2	$ 22.1	42.9	23.5	13.2	23.3	150.0	102.9	87.1
Assets
Other current assets	56.8				29.7				56.8	29.7
Property and equipment, net	5,808.9				5,427.6				5,808.9	5,427.6
Other assets	190.3				175.6				190.3	175.6
Liabilities
Deferred revenue, current	174.9				162.9				174.9	162.9
Deferred revenue, non-current	1,148.1				1,076.3				1,148.1	1,076.3
Deferred income taxes, net	134.9				147.1				134.9	147.1
Stockholders' equity
Accumulated deficit	$ (216.0)				(366.0)				$ (216.0)	(366.0)
Accounting Standards Update 2014-09 [Member] | Pro Forma [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
Accounting Standards Update 2014-09 [Member] | Effect of Adoption
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
As Reported
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)
As Adjusted | Accounting Standards Update 2014-09 [Member]
Assets
Other current assets					29.7					29.7
Property and equipment, net					5,427.6					5,427.6
Other assets					175.6					175.6
Liabilities
Deferred revenue, current					162.9					162.9
Deferred revenue, non-current					1,076.3					1,076.3
Deferred income taxes, net					147.1					147.1
Stockholders' equity
Accumulated deficit					$ (366.0)					$ (366.0)