Acquisitions (Schedule of Acquisition) (Details) - USD ($) $ in Millions						9 Months Ended
	Mar. 01, 2017	Oct. 03, 2016	Apr. 01, 2016	Jan. 15, 2016	Dec. 31, 2015	Mar. 31, 2017	Jun. 30, 2016
Business Acquisition [Line Items]
Goodwill						$ 1,822.6	$ 1,214.5
Electric Lightwave
Business Acquisition [Line Items]
Cash	$ 12.5
Other current assets	56.0
Property and equipment	489.5
Deferred tax assets, net	49.7
Intangibles	312.2
Goodwill	625.2
Other assets	1.7
Total assets acquired	1,546.8
Current liabilities	56.7
Deferred revenue	49.7
Other liabilities	1.2
Total liabilities assumed	107.6
Net assets acquired	1,439.2
Less cash acquired	(12.5)
Total consideration paid/payable	$ 1,426.7
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 assets acquired		11.3
Total consideration paid/payable		$ 11.3				$ 2.3
Clearview
Business Acquisition [Line Items]
Other current assets			$ 0.6
Property and equipment			17.1
Deferred tax assets, net			0.2
Intangibles			9.8
Goodwill			2.1
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
Total consideration paid/payable			$ 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)
Total consideration paid/payable				$ 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)
Total consideration paid/payable					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
Total consideration paid/payable					$ 16.6