Acquisitions (Narrative) (Details) € in Millions, CAD in Millions, $ in Millions								1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 01, 2017 USD ($) building item mi Center	Oct. 03, 2016 USD ($) ft² item MW	Apr. 01, 2016 USD ($) ft² item	Jan. 15, 2016 CAD building item mi	Jan. 15, 2016 USD ($) building item mi	Dec. 31, 2015 EUR (€) ft²	Dec. 31, 2015 USD ($) ft²	Mar. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) item	Mar. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of business combinations completed | item											40
Net consideration paid											$ 1,426.8	$ 417.0
Acquisition related costs									$ 8.4	$ 14.2	17.6	$ 17.5
Electric Lightwave
Business Acquisition [Line Items]
Net consideration paid	$ 1,426.7
Total consideration paid/payable	1,426.7
Amount of cash consideration to be paid								$ 2.2
Purchase price, held in escrow	$ 14.0
Number of data centers | Center	100
Long-Haul Fiber Network Acquired | mi	8,100
Metro Fiber Network Acquired | mi	4,000
Network concentrating net buildings | building	3,100
Number of metropolitan markets | item	35
Santa Clara Data Center
Business Acquisition [Line Items]
Total consideration paid/payable		$ 11.3									2.3
Number of quarterly payments | item		10
Amount of quarterly payments		$ 1.3
Amount of cash consideration to be paid											10.2
Acquired facility size (in square feet) | ft²		26,900
Acquired megawatts of critical power | MW		3
Clearview
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired			100.00%
Net consideration paid			$ 18.3
Total consideration paid/payable			$ 18.3
Acquired facility size (in square feet) | ft²			30,000
Number of data centers | item			2
Allstream
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired					100.00%
Net consideration paid				CAD 422.9	$ 297.6
Total consideration paid/payable					297.6
Working capital and other liabilities assumed in the acquisition					$ 29.6
Additional Route Miles Acquired | mi				18,000	18,000
Long-Haul Fiber Network Acquired | mi				12,500	12,500
Metro Fiber Network Acquired | mi				5,500	5,500
Network concentrating net buildings | building				3,300	3,300
Number of metropolitan markets | item				5	5
Other post retirement benefits plan liability assumed					$ 8.3						12.9
Viatel
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired						100.00%	100.00%
Net consideration paid						€ 92.9	$ 101.2
Total consideration paid/payable							101.2
Refund of escrow reflected as a cash inflow from investing activities											$ 1.5
Dallas Data Center
Business Acquisition [Line Items]
Net consideration paid							16.6
Total consideration paid/payable							$ 16.6
Acquired facility size (in square feet) | ft²						36,000	36,000