Acquisitions (Schedule of Acquisition) (Details) - USD ($) $ in Millions	Apr. 01, 2016	Jan. 15, 2016	Dec. 31, 2015	Sep. 30, 2016	Jun. 30, 2016
Business Acquisition [Line Items]
Goodwill				$ 1,210.6	$ 1,214.5
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	3.9
Other assets	0.2
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		102.2
Property and equipment		262.3
Deferred tax assets, net		2.4
Intangibles		64.5
Other assets		4.5
Total assets acquired		438.8
Current liabilities		64.6
Deferred revenue		46.2
Other liabilities		27.5
Total liabilities assumed		138.3
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			12.0
Property and equipment			162.3
Goodwill			13.0
Other assets			2.1
Total assets acquired			192.9
Current liabilities			17.6
Deferred revenue			57.8
Deferred tax liability, net			5.7
Other liabilities			7.1
Total liabilities assumed			88.2
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			14.8
Intangibles			1.8
Total assets acquired			16.6
Net assets acquired			16.6
Net consideration paid			$ 16.6