Acquisitions (Narrative) (Details) € in Millions, CAD in Millions, $ in Millions							3 Months Ended		6 Months Ended
	Oct. 03, 2016 USD ($) ft² payment MW	Apr. 01, 2016 USD ($) 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	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) ft²	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) ft²
Business Acquisition [Line Items]
Number of business combinations completed | item									39
Net consideration paid									$ 1.3	$ 117.7
Acquisition related costs							$ 6.2	$ 3.3	9.2	$ 3.3
Santa Clara Data Center
Business Acquisition [Line Items]
Net consideration paid	$ 12.8
Net consideration paid	$ 11.3
Number of quarterly payments | payment	10
Amount of quarterly payments	$ 1.3
Amount of cash consideration to be paid									11.5
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
Net consideration paid		$ 18.3
Acquired facility size (in square feet) | ft²		30,000
Purchase price, held in escrow		$ 1.1
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
Net consideration paid				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%		100.00%		100.00%
Net consideration paid					€ 92.9	$ 101.2
Net consideration paid						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
Net consideration paid						$ 16.6
Acquired facility size (in square feet) | ft²					36,000	36,000		36,000		36,000