Segment Reporting (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenue from external customers	$ 369.6	$ 323.9	$ 736.4	$ 644.5
Segment Adjusted EBITDA	218.9	189.7	434.3	372.7
Total assets	6,273.5	4,989.2	6,273.5	4,989.2	$ 6,094.6
Capital expenditures	172.4	129.5	331.6	244.8
Reportable Segments [Member] | Dark Fiber Solutions [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	137.7	129.7	272.7	257.1
Segment Adjusted EBITDA	99.1	89.6	195.7	174.8
Total assets	3,078.3	2,652.1	3,078.3	2,652.1	2,830.1
Capital expenditures	109.2	69.7	202.7	127.8
Reportable Segments [Member] | Network Connectivity [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	168.7	161.7	335.7	321.9
Segment Adjusted EBITDA	89.9	85.6	178.6	168.7
Total assets	1,900.7	1,766.3	1,900.7	1,766.3	1,807.7
Capital expenditures	48.1	52.5	94.8	98.8
Reportable Segments [Member] | Colocation and Cloud Infrastructure [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	58.5	27.0	116.8	53.9
Segment Adjusted EBITDA	29.0	13.4	57.4	26.7
Total assets	1,027.2	250.1	1,027.2	250.1	1,032.6
Capital expenditures	15.1	7.3	34.1	18.2
Reportable Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	4.7	5.5	11.2	11.6
Segment Adjusted EBITDA	0.9	1.1	2.6	2.5
Total assets	34.4	36.1	34.4	36.1	35.0
Corporate/eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 232.9	$ 284.6	$ 232.9	$ 284.6	$ 389.2