CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Schedule Of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015
Current assets
Cash and cash equivalents	$ 197.7	$ 170.1	$ 214.7	$ 308.0
Trade receivables, net of allowance	189.7	148.4
Prepaid expenses	72.4	68.8
Other assets	36.7	9.3
Total current assets	496.5	396.6
Property and equipment, net	4,839.5	4,079.5
Intangible assets, net	1,196.6	934.9
Goodwill	1,822.6	1,214.5
Deferred income taxes, net	51.8
Other assets	129.8	94.5
Total assets	8,536.8	6,720.0
Current liabilities
Current portion of long-term debt	25.0
Accounts payable	50.2	97.0
Accrued liabilities	289.8	226.9
Accrued interest	75.3	28.6
Capital lease obligations, current	7.8	5.8
Deferred revenue, current	144.2	129.4
Total current liabilities	592.3	487.7
Long-term debt, non-current	5,498.8	4,085.3
Capital lease obligation, non-current	76.5	44.9
Deferred revenue, non-current	940.6	793.3
Deferred income taxes, net	40.0	48.0
Other long-term liabilities	59.0	57.0
Total liabilities	7,207.2	5,516.2
Member's Equity
Member's interest	1,861.3	1,772.6
Accumulated other comprehensive (loss)/income	(19.2)	4.5
Accumulated deficit	(512.5)	(573.3)
Total member's equity	1,329.6	1,203.8
Total liabilities and member's equity	8,536.8	6,720.0
Eliminations [Member]
Current assets
Related party receivable	(330.2)	(346.7)
Investment in subsidiary	(586.5)	(550.9)
Total assets	(916.7)	(897.6)
Current liabilities
Related party debt, long-term	(330.2)	(346.7)
Total liabilities	(330.2)	(346.7)
Member's Equity
Member's interest	(587.7)	(579.1)
Accumulated deficit	1.2	28.2
Total member's equity	(586.5)	(550.9)
Total liabilities and member's equity	(916.7)	(897.6)
Zayo Group, LLC [Member]
Current assets
Cash and cash equivalents	104.6	91.3	131.2	275.9
Trade receivables, net of allowance	116.3	75.5
Prepaid expenses	45.3	33.7
Other assets	39.9	(2.0)
Total current assets	306.1	198.5
Property and equipment, net	4,151.9	3,375.7
Intangible assets, net	1,044.2	775.5
Goodwill	1,650.5	1,025.5
Deferred income taxes, net	51.8
Other assets	105.6	65.0
Related party receivable	330.2	346.7
Investment in subsidiary	586.5	550.9
Total assets	8,226.8	6,337.8
Current liabilities
Current portion of long-term debt	25.0
Accounts payable	36.7	70.3
Accrued liabilities	207.0	116.0
Accrued interest	75.3	28.6
Capital lease obligations, current	6.6	4.2
Deferred revenue, current	109.8	89.1
Total current liabilities	460.4	308.2
Long-term debt, non-current	5,498.8	4,085.3
Capital lease obligation, non-current	66.1	32.0
Deferred revenue, non-current	839.4	681.1
Deferred income taxes, net	0.1	3.3
Other long-term liabilities	32.4	24.1
Total liabilities	6,897.2	5,134.0
Member's Equity
Member's interest	1,884.1	1,786.2
Accumulated other comprehensive (loss)/income	(32.9)
Accumulated deficit	(521.6)	(582.4)
Total member's equity	1,329.6	1,203.8
Total liabilities and member's equity	8,226.8	6,337.8
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	2.2	3.0	3.5	3.1
Trade receivables, net of allowance	2.0	2.1
Prepaid expenses	0.4	0.3
Total current assets	4.6	5.4
Intangible assets, net	11.5	12.9
Goodwill	14.7	14.6
Total assets	30.8	32.9
Current liabilities
Accrued liabilities	0.6	0.7
Deferred revenue, current	0.2	0.2
Total current liabilities	0.8	0.9
Total liabilities	0.8	0.9
Member's Equity
Member's interest	18.7	22.3
Accumulated deficit	11.3	9.7
Total member's equity	30.0	32.0
Total liabilities and member's equity	30.8	32.9
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	90.9	75.8	$ 80.0	$ 29.0
Trade receivables, net of allowance	71.4	70.8
Prepaid expenses	26.7	34.8
Other assets	(3.2)	11.3
Total current assets	185.8	192.7
Property and equipment, net	687.6	703.8
Intangible assets, net	140.9	146.5
Goodwill	157.4	174.4
Other assets	24.2	29.5
Total assets	1,195.9	1,246.9
Current liabilities
Accounts payable	13.5	26.7
Accrued liabilities	82.2	110.2
Capital lease obligations, current	1.2	1.6
Deferred revenue, current	34.2	40.1
Total current liabilities	131.1	178.6
Related party debt, long-term	330.2	346.7
Capital lease obligation, non-current	10.4	12.9
Deferred revenue, non-current	101.2	112.2
Deferred income taxes, net	39.9	44.7
Other long-term liabilities	26.6	32.9
Total liabilities	639.4	728.0
Member's Equity
Member's interest	546.2	543.2
Accumulated other comprehensive (loss)/income	13.7	4.5
Accumulated deficit	(3.4)	(28.8)
Total member's equity	556.5	518.9
Total liabilities and member's equity	$ 1,195.9	$ 1,246.9