CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Schedule of Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018
Current assets
Cash and cash equivalents	$ 253.9	$ 185.4	$ 353.2	$ 256.0
Trade receivables, net of allowance	151.9	177.0
Prepaid expenses	68.1	65.3
Other current assets	57.0	56.8
Total current assets	530.9	484.5
Property and equipment, net	5,851.8	5,808.9
Intangible assets, net	1,092.8	1,118.8
Goodwill	1,701.1	1,706.6
Right-of-use operating lease assets	499.2
Deferred income taxes, net	21.3	24.8
Other assets	184.0	190.2
Total assets	9,881.1	9,333.8
Current liabilities
Accounts payable	31.9	73.7
Accrued liabilities	323.6	314.8
Accrued interest	84.9	73.1
Current portion of long-term debt	130.0	5.0
Operating lease obligations, current	127.2
Finance lease obligations, current	9.5	10.0
Deferred revenue, current	172.9	174.9
Total current liabilities	880.0	651.5
Long-term debt, non-current	5,696.1	5,839.7
Operating lease liabilities, non-current	387.4
Finance lease obligation, non-current	176.0	172.2
Deferred revenue, non-current	1,205.4	1,148.1
Deferred income taxes, net	147.5	138.8
Other long-term liabilities	30.1	54.7
Total liabilities	8,522.5	8,005.0
Member's equity
Member's interest	1,602.5	1,576.2
Accumulated other comprehensive loss	(38.3)	(23.9)
Accumulated deficit	(205.6)	(223.5)
Total member's equity	1,358.6	1,328.8	$ 1,542.1	$ 1,487.6
Total liabilities and member's equity	9,881.1	9,333.8
Eliminations [Member]
Current assets
Related party receivable		(358.9)
Investment in subsidiary	(635.2)	(664.1)
Total assets	(635.2)	(1,023.0)
Current liabilities
Related party debt, long-term		(358.9)
Total liabilities		(358.9)
Member's equity
Member's interest	(464.6)	(487.3)
Accumulated other comprehensive loss	38.3	23.9
Accumulated deficit	(208.9)	(200.7)
Total member's equity	(635.2)	(664.1)
Total liabilities and member's equity	(635.2)	(1,023.0)
Zayo Group, LLC [Member]
Current assets
Cash and cash equivalents	145.1	85.9
Trade receivables, net of allowance	92.5	97.7
Prepaid expenses	55.1	47.9
Other current assets	129.8	131.4
Total current assets	422.5	362.9
Property and equipment, net	5,055.9	5,010.1
Intangible assets, net	963.3	983.7
Goodwill	1,520.4	1,520.3
Right-of-use operating lease assets	328.7
Deferred income taxes, net		1.0
Other assets	149.3	152.4
Related party receivable		358.9
Investment in subsidiary	635.2	664.1
Total assets	9,075.3	9,053.4
Current liabilities
Accounts payable	15.7	53.2
Accrued liabilities	260.3	243.4
Accrued interest	84.9	73.1
Current portion of long-term debt	130.0	5.0
Operating lease obligations, current	95.7
Finance lease obligations, current	8.3	8.6
Deferred revenue, current	135.0	135.1
Total current liabilities	729.9	518.4
Long-term debt, non-current	5,318.4	5,839.7
Operating lease liabilities, non-current	252.1
Finance lease obligation, non-current	167.5	163.4
Deferred revenue, non-current	1,104.0	1,045.2
Deferred income taxes, net	144.1	136.6
Other long-term liabilities	0.7	21.3
Total liabilities	7,716.7	7,724.6
Member's equity
Member's interest	1,611.5	1,587.4
Accumulated other comprehensive loss	(38.3)	(23.9)
Accumulated deficit	(214.6)	(234.7)
Total member's equity	1,358.6	1,328.8
Total liabilities and member's equity	9,075.3	9,053.4
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	7.4	9.6
Trade receivables, net of allowance	1.4	2.6
Prepaid expenses	0.2	0.1
Total current assets	9.0	12.3
Intangible assets, net	6.9	7.3
Goodwill	14.6	14.6
Right-of-use operating lease assets	1.9
Total assets	32.4	34.2
Current liabilities
Accounts payable	0.1	0.5
Accrued liabilities	0.8	1.4
Operating lease obligations, current	1.8
Deferred revenue, current	0.1	0.1
Total current liabilities	2.8	2.0
Total liabilities	2.8	2.0
Member's equity
Member's interest	10.1	13.5
Accumulated deficit	19.5	18.7
Total member's equity	29.6	32.2
Total liabilities and member's equity	32.4	34.2
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	101.4	89.9
Trade receivables, net of allowance	58.0	76.7
Prepaid expenses	12.8	17.3
Other current assets	(72.8)	(74.6)
Total current assets	99.4	109.3
Property and equipment, net	795.9	798.8
Intangible assets, net	122.6	127.8
Goodwill	166.1	171.7
Right-of-use operating lease assets	168.6
Deferred income taxes, net	21.3	23.8
Other assets	34.7	37.8
Total assets	1,408.6	1,269.2
Current liabilities
Accounts payable	16.1	20.0
Accrued liabilities	62.5	70.0
Operating lease obligations, current	29.7
Finance lease obligations, current	1.2	1.4
Deferred revenue, current	37.8	39.7
Total current liabilities	147.3	131.1
Long-term debt, non-current	377.7
Operating lease liabilities, non-current	135.3
Finance lease obligation, non-current	8.5	8.8
Related party debt, long-term		358.9
Deferred revenue, non-current	101.4	102.9
Deferred income taxes, net	3.4	2.2
Other long-term liabilities	29.4	33.4
Total liabilities	803.0	637.3
Member's equity
Member's interest	445.5	462.6
Accumulated other comprehensive loss	(38.3)	(23.9)
Accumulated deficit	198.4	193.2
Total member's equity	605.6	631.9
Total liabilities and member's equity	$ 1,408.6	$ 1,269.2