ACQUISITIONS AND DISPOSITIONS (Narrative) (Details) $ in Millions, $ in Millions							3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2018 USD ($)	Jan. 18, 2018 CAD ($)	Jan. 18, 2018 USD ($)	May 01, 2017 USD ($)	Mar. 01, 2017 USD ($)	Oct. 03, 2016 USD ($) item	Mar. 31, 2018 CAD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) item	Mar. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Business Acquisition [Line Items]
Number of business combinations completed | item											43
Increase (decrease) in intangible assets								$ (56.3)			$ 103.9
Increase in property plant and equipment								77.4			129.6
Increase in deferred tax liability								29.8
Increase in depreciation and amortization								1.2			16.6
Increase in depreciation and amortization early reported										$ 1.0			$ 5.5
Acquisition related costs								3.3	$ 8.4		17.5	$ 17.6
Net consideration paid											155.3	$ 1,424.5
Spread Networks
Business Acquisition [Line Items]
Business acquisition purchase price	$ 130.5
Purchase price, held in escrow								6.4
Post-acquisition period revenue recognized								1.7
Optic Zoo Networks
Business Acquisition [Line Items]
Business acquisition purchase price		$ 30.9	$ 24.8
Purchase price, held in escrow							$ 3.8	2.9
Post-acquisition period revenue recognized								0.7
KIO Networks US Data Centers
Business Acquisition [Line Items]
Business acquisition purchase price				$ 11.9
Purchase price, held in escrow								1.2
Electric Lightwave
Business Acquisition [Line Items]
Business acquisition purchase price					$ 1,426.6
Purchase price, held in escrow								1.7
Net consideration paid					$ 1,426.6
Santa Clara Data Center
Business Acquisition [Line Items]
Business acquisition purchase price						$ 11.3
Remaining cash consideration to be paid								$ 5.1
Number of quarterly payments | item						10
Amount of quarterly payments						$ 1.3					$ 3.8