ACQUISITIONS AND DISPOSITIONS (Schedule of Acquisition) (Details) $ in Millions, $ in Millions	Feb. 28, 2018 USD ($)	Jan. 18, 2018 CAD ($)	Jan. 18, 2018 USD ($)	May 01, 2017 USD ($)	Mar. 01, 2017 USD ($)	Oct. 03, 2016 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill							$ 1,735.5	$ 1,840.2
Spread Networks
Business Acquisition [Line Items]
Cash	$ 1.5
Other current assets	3.0
Property and equipment	133.7
Intangibles	19.8
Goodwill	23.3
Other assets	1.4
Total assets acquired	182.7
Current liabilities	3.7
Deferred revenue	27.2
Other liabilities	19.8
Total liabilities assumed	50.7
Net assets acquired	132.0
Less cash acquired	(1.5)
Total consideration paid/payable	$ 130.5
Optic Zoo Networks
Business Acquisition [Line Items]
Cash			$ 1.4
Other current assets			0.3
Property and equipment			13.6
Intangibles			5.2
Goodwill			9.2
Other assets			0.2
Total assets acquired			29.9
Current liabilities			0.6
Deferred tax liability, net			1.8
Deferred revenue			1.3
Total liabilities assumed			3.7
Net assets acquired			26.2
Less cash acquired			(1.4)
Total consideration paid/payable		$ 30.9	$ 24.8
KIO Networks US Data Centers
Business Acquisition [Line Items]
Cash				$ 0.1
Property and equipment				2.4
Deferred tax assets, net				2.9
Intangibles				6.4
Goodwill				2.7
Other assets				0.6
Total assets acquired				15.1
Current liabilities				1.7
Deferred revenue				0.5
Total liabilities assumed				2.2
Net assets acquired				12.9
Less cash acquired				(0.1)
Impact of U.S Tax Reform				(0.9)
Total consideration paid/payable				$ 11.9
Electric Lightwave
Business Acquisition [Line Items]
Cash					$ 12.6
Other current assets					55.0
Property and equipment					650.2
Intangibles					416.1
Goodwill					488.0
Other assets					1.7
Total assets acquired					1,623.6
Current liabilities					61.7
Capital lease obligations					64.9
Deferred revenue					80.0
Other liabilities					1.2
Total liabilities assumed					207.8
Net assets acquired					1,415.8
Less cash acquired					(12.6)
Impact of U.S Tax Reform					23.4
Total consideration paid/payable					$ 1,426.6
Santa Clara Data Center
Business Acquisition [Line Items]
Property and equipment						$ 31.9
Intangibles						6.0
Total assets acquired						37.9
Deferred tax liability, net						26.6
Total liabilities assumed						26.6
Net assets acquired						11.3
Total consideration paid/payable						$ 11.3