Acquisitions (Schedule of Acquisition) (Details) - USD ($) $ in Millions	Oct. 03, 2016	Apr. 01, 2016	Jan. 15, 2016	Dec. 31, 2015	Dec. 31, 2016	Jun. 30, 2016
Business Acquisition [Line Items]
Goodwill					$ 1,196.9	$ 1,214.5
Santa Clara Data Center
Business Acquisition [Line Items]
Property and equipment	$ 35.1
Intangibles	2.8
Total assets acquired	37.9
Capital lease obligations	26.6
Total liabilities assumed	26.6
Net consideration paid	$ 11.3
Clearview
Business Acquisition [Line Items]
Other current assets		$ 0.6
Property and equipment		15.4
Deferred tax assets, net		0.2
Intangibles		9.8
Goodwill		3.8
Other assets		0.3
Total assets acquired		30.1
Current liabilities		1.1
Deferred revenue		0.4
Other liabilities		10.3
Total liabilities assumed		11.8
Net assets acquired		18.3
Net consideration paid		$ 18.3
Allstream
Business Acquisition [Line Items]
Cash			$ 2.9
Other current assets			95.6
Property and equipment			266.3
Deferred tax assets, net			3.8
Intangibles			64.5
Other assets			4.5
Total assets acquired			437.6
Current liabilities			63.2
Deferred revenue			46.9
Other liabilities			27.0
Total liabilities assumed			137.1
Net assets acquired			300.5
Less cash acquired			(2.9)
Net consideration paid			$ 297.6
Viatel
Business Acquisition [Line Items]
Cash				$ 3.5
Other current assets				7.3
Property and equipment				174.0
Goodwill				9.5
Other assets				2.0
Total assets acquired				196.3
Current liabilities				18.8
Deferred revenue				58.5
Deferred tax liability, net				8.6
Other liabilities				5.7
Total liabilities assumed				91.6
Net assets acquired				104.7
Less cash acquired				(3.5)
Net consideration paid				101.2
Dallas Data Center
Business Acquisition [Line Items]
Property and equipment				12.2
Intangibles				4.4
Total assets acquired				16.6
Net assets acquired				16.6
Net consideration paid				$ 16.6