ACQUISITIONS (Narrative) (Details) $ in Millions					3 Months Ended			6 Months Ended
	Nov. 26, 2017 USD ($) mi	May 01, 2017 USD ($) ft² Center MW	Mar. 01, 2017 USD ($) building item mi Center	Oct. 03, 2016 USD ($) ft² item MW	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of business combinations completed | item								41
Increase in intangible assets					$ 160.2
Increase in property plant and equipment					52.2
Decrease in deferred tax assets								$ 80.2
Decrease in depreciation and amortization					(12.1)	$ (12.1)
Decrease in depreciation and amortization early reported						$ 8.4			$ 4.8
Acquisition related costs					$ 5.9		$ 6.2	14.2		$ 9.2
Net consideration paid										$ 1.3
Spread Networks
Business Acquisition [Line Items]
Business acquisition purchase price	$ 127.0
Spread Networks | Long Haul Fiber [Member]
Business Acquisition [Line Items]
Additional Route Miles Acquired | mi	825
KIO Networks US Data Centers
Business Acquisition [Line Items]
Business acquisition purchase price		$ 11.9
Acquired facility size (in square feet) | ft²		100,000
Acquired megawatts of critical power | MW		2
Purchase price, held in escrow		$ 1.2
Number of data centers | Center		2
Electric Lightwave
Business Acquisition [Line Items]
Business acquisition purchase price			$ 1,426.6
Purchase price, held in escrow			$ 7.0
Number of metropolitan markets | item			35
Net Buildings Concentrating Network | building			3,100
Number of data centers | Center			100
Net consideration paid			$ 1,426.6
Electric Lightwave | Long Haul Fiber [Member]
Business Acquisition [Line Items]
Additional Route Miles Acquired | mi			8,100
Electric Lightwave | Metro Fiber [Member]
Business Acquisition [Line Items]
Additional Route Miles Acquired | mi			4,000
Santa Clara Data Center
Business Acquisition [Line Items]
Business acquisition purchase price				$ 11.3
Acquired facility size (in square feet) | ft²				26,900
Acquired megawatts of critical power | MW				3
Remaining cash consideration to be paid				$ 6.4
Number of quarterly payments | item				10
Amount of quarterly payments				$ 1.3				$ 2.5