Segment Reporting (Summary of Financial Information by Segments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenue from external customers	$ 478.0	$ 340.7	$ 1,214.4	$ 985.2
Segment Adjusted EBITDA	242.8	199.0	677.1	571.7
Total assets	6,833.2	5,991.9	6,833.2	5,991.9	$ 6,094.6
Capital expenditures	185.1	130.1	516.7	374.9
Reportable Segments [Member] | Dark Fiber Solutions [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	144.3	133.5	417.0	390.6
Segment Adjusted EBITDA	103.9	92.5	299.6	267.3
Total assets	3,139.0	2,754.2	3,139.0	2,754.2	2,848.9
Capital expenditures	110.3	73.1	313.0	200.9
Reportable Segments [Member] | Network Connectivity [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	172.5	163.1	508.2	485.0
Segment Adjusted EBITDA	89.2	85.7	267.8	254.4
Total assets	1,890.1	1,794.0	1,890.1	1,794.0	1,807.7
Capital expenditures	44.2	46.9	139.0	145.7
Reportable Segments [Member] | Colocation and Cloud Infrastructure [ Member ]
Segment Reporting Information [Line Items]
Revenue from external customers	60.3	38.5	177.1	92.4
Segment Adjusted EBITDA	30.2	19.5	87.6	46.2
Total assets	1,040.7	1,013.6	1,040.7	1,013.6	1,013.7
Capital expenditures	19.5	10.1	53.6	28.3
Reportable Segments [Member] | Zayo Canada [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	96.1		96.1
Segment Adjusted EBITDA	18.2		18.2
Total assets	452.7		452.7
Capital expenditures	11.1		11.1
Reportable Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue from external customers	4.8	5.6	16.0	17.2
Segment Adjusted EBITDA	1.3	1.3	3.9	3.8
Total assets	33.9	38.6	33.9	38.6	35.0
Corporate/eliminations [Member]
Segment Reporting Information [Line Items]
Total assets	$ 276.8	$ 391.5	$ 276.8	$ 391.5	$ 389.3