Acquisitions (Schedule of Acquisition) (Details) - USD ($) $ in Millions	May 01, 2017	Mar. 01, 2017	Oct. 03, 2016	Apr. 01, 2016	Jan. 15, 2016	Dec. 31, 2015	Feb. 23, 2015	Jan. 01, 2015	Jul. 01, 2014	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Business Acquisition [Line Items]
Goodwill										$ 1,840.2	$ 1,214.5	$ 1,224.4
KIO Networks US Data Centers
Business Acquisition [Line Items]
Cash	$ 0.1
Other current assets	0.1
Property and equipment	2.4
Intangibles	6.4
Goodwill	6.0
Other assets	0.5
Total assets acquired	15.5
Current liabilities	1.7
Deferred tax liability, net	1.3
Deferred revenue	0.5
Total liabilities assumed	3.5
Net assets acquired	12.0
Less cash acquired	(0.1)
Total consideration paid/payable	$ 11.9
Electric Lightwave
Business Acquisition [Line Items]
Cash		$ 12.6
Other current assets		55.4
Property and equipment		520.6
Deferred tax assets, net		46.7
Intangibles		312.2
Goodwill		629.3
Other assets		1.7
Total assets acquired		1,578.5
Current liabilities		58.1
Deferred revenue		80.0
Other liabilities		1.2
Total liabilities assumed		139.3
Net assets acquired		1,439.2
Less cash acquired		(12.6)
Total consideration paid/payable		$ 1,426.6
Santa Clara Data Center
Business Acquisition [Line Items]
Property and equipment			$ 31.9
Intangibles			6.0
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
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 tax liability, net						8.6
Deferred revenue						58.5
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
Atlanta NAP
Business Acquisition [Line Items]
Other current assets									$ 0.2
Property and equipment									7.0
Intangibles									21.0
Goodwill									25.2
Total assets acquired									53.4
Current liabilities									1.5
Total liabilities assumed									1.5
Net assets acquired									51.9
Total consideration paid/payable									51.9
Neo Telecoms
Business Acquisition [Line Items]
Cash									4.2
Other current assets									9.5
Property and equipment									31.3
Intangibles									26.4
Goodwill									32.5
Other assets									2.3
Total assets acquired									106.2
Current liabilities									13.5
Deferred tax liability, net									7.6
Deferred revenue									3.7
Other liabilities									3.3
Total liabilities assumed									28.1
Net assets acquired									78.1
Less cash acquired									(4.2)
Total consideration paid/payable									$ 73.9
Ideatek Systems, Inc
Business Acquisition [Line Items]
Other current assets								$ 0.8
Property and equipment								32.3
Deferred tax assets, net								3.1
Intangibles								7.6
Goodwill								39.0
Total assets acquired								82.8
Current liabilities								4.4
Deferred revenue								25.7
Total liabilities assumed								30.1
Net assets acquired								52.7
Total consideration paid/payable								$ 52.7
Latisys Holdings, LLC
Business Acquisition [Line Items]
Cash							$ 9.4
Other current assets							17.4
Property and equipment							222.9
Deferred tax assets, net							0.4
Intangibles							250.2
Goodwill							274.1
Other assets							5.0
Total assets acquired							779.4
Current liabilities							9.9
Deferred tax liability, net							79.1
Deferred revenue							3.2
Total liabilities assumed							92.2
Net assets acquired							687.2
Less cash acquired							(9.4)
Total consideration paid/payable							$ 677.8