QUARTERLY FINANCIAL DATA (Schedule of Quarterly Results) (Details) - USD ($) $ / shares in Units, $ 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
QUARTERLY FINANCIAL DATA
Revenue	$ 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 and expenses
Operating costs (excluding depreciation and amortization and including stock-based compensation—Note 11)	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 (including stock-based compensation—Note 11)	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
Total operating costs and expenses	529.4	515.6	494.4	518.3	538.3	543.5	549.9	547.6	2,057.7	2,179.3	1,844.3
Operating income	121.2	131.6	144.7	122.8	119.0	105.5	103.2	95.5	520.3	423.2	376.0
Other expenses
Interest expense	(86.1)	(86.4)	(84.0)	(82.2)	(77.8)	(75.3)	(73.1)	(73.6)	(338.7)	(299.8)	(241.5)
Loss on extinguishment of debt								(4.9)		(4.9)	(18.2)
Foreign currency (loss)/gain on intercompany loans	(8.3)	7.1	(8.3)	(4.6)	(22.4)	13.9	3.1	10.8	(14.1)	5.4	(10.3)
Other income, net	0.5	0.4	0.3	6.6	0.7	0.4	0.4	0.9	7.8	2.4	0.3
Total other expenses, net	(93.9)	(78.9)	(92.0)	(80.2)	(99.5)	(61.0)	(69.6)	(66.8)	(345.0)	(296.9)	(269.7)
Income from operations before income taxes	27.3	52.7	52.7	42.6	19.5	44.5	33.6	28.7	175.3	126.3	106.3
Provision/(benefit) 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
Net income per share:
Basic (in dollars per share)	$ 0.27	$ 0.15	$ 0.13	$ 0.09	$ 0.17	$ 0.09	$ 0.05	$ 0.09	$ 0.63	$ 0.42	$ 0.36
Diluted (in dollars per share)	$ 0.26	$ 0.15	$ 0.13	$ 0.09	$ 0.17	$ 0.09	$ 0.05	$ 0.09	$ 0.62	$ 0.41	$ 0.35
Provisional tax expense (benefit) to record the impact of U.S. Tax Reform					$ (23.9)	$ 4.6	$ 44.1		$ 7.2	$ 24.8