Segment Reporting (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenue from external customers	$ 638.0	$ 550.2	$ 506.7	$ 504.9	$ 507.3	$ 478.0	$ 369.6	$ 366.8	$ 2,199.8	$ 1,721.7	$ 1,347.1
Segment Adjusted EBITDA									1,116.8	934.9	782.6
Total assets	8,739.4				6,727.5				8,739.4	6,727.5
Capital expenditures									835.5	704.1	530.4
Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									722.1
Segment Adjusted EBITDA									566.3
Total assets	4,504.6								4,504.6
Capital expenditures									499.1
Parent Company [Member]
Segment Reporting Information [Line Items]
Total assets	0.0								0.0
Reportable Segments [Member] | Fiber Solutions [Member]
Segment Reporting Information [Line Items]
Revenue from external customers										648.8	575.6
Segment Adjusted EBITDA										499.6	400.7
Total assets					3,780.9					3,780.9
Capital expenditures										421.4	303.5
Reportable Segments [Member] | Transport [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									440.4	391.4	336.4
Segment Adjusted EBITDA									184.2	168.0	139.3
Total assets	1,230.0				964.8				1,230.0	964.8
Capital expenditures									147.3	123.1	110.6
Reportable Segments [Member] | Enterprise Networks [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									487.4	359.6	285.0
Segment Adjusted EBITDA									178.0	145.6	172.8
Total assets	1,385.7				849.2				1,385.7	849.2
Capital expenditures									89.1	88.0	62.8
Reportable Segments [Member] | zColo [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									214.0	195.4	126.9
Segment Adjusted EBITDA									111.9	100.9	64.7
Total assets	994.4				884.3				994.4	884.3
Capital expenditures									91.5	66.3	53.5
Reportable Segments [Member] | Allstream
Segment Reporting Information [Line Items]
Revenue from external customers									314.3	106.2
Segment Adjusted EBITDA									71.3	16.3
Total assets	406.2				72.6				406.2	72.6
Capital expenditures									8.5	5.3
Reportable Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									21.6	20.3	23.2
Segment Adjusted EBITDA									5.1	4.5	$ 5.1
Total assets	33.2				33.5				33.2	33.5
Corp/Eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 185.3				$ 142.2				$ 185.3	$ 142.2