Quarterly Financial Data (Schedule of Quarterly Results) (Details) - USD ($) $ in Millions		3 Months Ended																6 Months Ended	9 Months Ended	12 Months Ended
	Jul. 02, 2012	Jun. 30, 2015	[1]	Mar. 31, 2015	[1],[2],[3]	Dec. 31, 2014	[1]	Sep. 30, 2014	[1]	Jun. 30, 2014	[4],[5]	Mar. 31, 2014	[4],[6]	Dec. 31, 2013	[4],[7],[8]	Sep. 30, 2013	[4]	Dec. 31, 2014	Mar. 31, 2015	Jun. 30, 2015		Jun. 30, 2014	[4]	Jun. 30, 2013
Quarterly Financial Data [Abstract]
Revenue		$ 361.9		$ 340.7		$ 323.9		$ 320.6		$ 296.7		$ 281.4		$ 277.0		$ 268.1		$ 644.5	$ 985.2	$ 1,347.1	[1]	$ 1,123.2		$ 1,004.4
Operating costs and expenses
Operating costs (excluding depreciation and amortization and including stock-based compensation)		107.5		100.9		97.8		107.3		93.1		85.1		86.0		80.0				413.5	[1]	344.2		313.7
Selling, general and administrative expenses (including stock-based compensation—Note 12)		86.5	[9]	83.0	[9]	32.1	[9]	156.8	[9]	125.6		96.3		86.7		76.1				358.4	[1],[9]	384.7		256.6
Depreciation and amortization		113.2		100.1		96.9		96.0		91.3		84.2		81.7		81.0				406.2	[1]	338.2		324.5
Total operating costs and expenses		307.2		284.0		226.8		360.1		310.0		265.6		254.4		237.1				1,178.1	[1]	1,067.1		894.8
Operating income		54.7		56.7		97.1		(39.5)		(13.3)		15.8		22.6		31.0				169.0	[1]	56.1		109.6
Other expenses
Interest expense		(53.0)		(60.7)		(53.4)		(46.9)		(52.6)	[10]	(49.1)	[10]	(50.3)	[10]	(51.5)	[10]			(214.0)	[1]	(203.5)	[10]	(202.5)
Loss on extinguishment of debt	$ (65.0)	(8.5)	[11]	(54.9)	[11]	(30.9)	[11]							(1.9)	[12]					(94.3)	[1],[11]	(1.9)	[12]	(77.3)
Foreign currency (loss)/gain on intercompany loans		16.8		(13.2)		(13.3)		(14.7)		3.8		0.1		0.2		0.6				(24.4)	[1]	4.7		0.1
Other (expense)/income, net		(0.3)				(0.1)								0.2		0.1				(0.4)	[1]	0.3		0.3
Total other expenses, net		(45.0)		(128.8)		(97.7)		(61.6)		(48.8)		(49.0)		(51.8)		(50.8)				(333.1)	[1]	(200.4)		(279.4)
Loss from operations before income taxes		9.7		(72.1)		(0.6)		(101.1)		(62.1)		(33.2)		(29.2)		(19.8)				(164.1)	[1]	(144.3)		(169.8)
(Benefit)/provision for income taxes		4.6		(18.4)		(4.4)		9.4		10.1		9.5		8.4		9.3				(8.8)	[1]	37.3		(24.2)
Loss from continuing operations										(72.2)		(42.7)		(37.6)		(29.1)				(155.3)		(181.6)		(145.6)
Earnings from discontinued operations, net of income taxes										(1.3)	[13]	1.1	[13]	0.8	[13]	1.7	[13]					2.3	[13]	8.4
Net loss		$ 5.1		$ (53.7)		$ 3.8		$ (110.5)		$ (73.5)		$ (41.6)		$ (36.8)		$ (27.4)				$ (155.3)	[1]	$ (179.3)		$ (137.2)

[1] The Company realized an increase in revenue and operating expenses beginning July 1, 2014 as a result of the acquisition of AtlantaNap and Neo.

[2] The Company realized an increase in revenue and operating expenses beginning February 23, 2015 as a result of the acquisition of Latisys.

[3] The Company realized an increase in revenue and operating expenses beginning January 1, 2015 as a result of the acquisition of IdeaTek.

[4] The Company realized an increase in revenue and operating expenses beginning August 1, 2013 as a result of the acquisition of Corelink.

[5] The Company realized an increase in revenue and operating expenses beginning May 16, 2014 as a result of the acquisition of Geo.

[6] The Company realized an increase in revenue and operating expenses beginning March 4, 2014 as a result of the acquisition of CoreXchange.

[7] The Company realized an increase in revenue and operating expenses beginning October 1, 2013 as a result of the acquisition of Access.

[8] The Company realized an increase in revenue and operating expenses beginning October 2, 2013 as a result of the acquisition of Fiberlink.

[9] The Company realized an increase in compensation expense in the first quarter as a result of an increase in the estimated fair value of CII common units as a result of the pending IPO. The common unit fair values were further adjusted in second quarter upon completion of the IPO. See Note 12— Stock-based Compensation.

[10] The Company realized an increase in interest expense during the second and fourth quarters of 2014 due to financing transactions completed to increase its borrowings under its term loan facility. See Note 8— Long-Term Debt.

[11] The Company completed debt refinancing transactions during the second, third and fourth quarters of Fiscal 2015, resulting in a loss on debt extinguishment for those respective periods. See Note 8— Long-Term Debt.

[12] The Company completed a debt refinancing transaction during the second quarter of Fiscal 2014, resulting in a loss on debt extinguishment for that period. See Note 8— Long-Term Debt.

[13] The Company spun-off its OVS operating unit on June 13, 2014.