CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Schedule Of Condensed Consolidating Statements Of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Net cash provided by operating activities			$ 664.9	$ 537.9
Cash flows from investing activities
Purchases of property and equipment	$ (208.3)	$ (185.1)	(630.2)	(516.7)
Acquisitions, net of cash acquired			(1,426.8)	(417.0)
Other			1.5
Net cash used in investing activities			(2,055.5)	(933.7)
Cash flows from financing activities
Proceeds from debt			3,293.8	395.2
Principal payments on long-term debt			(1,837.4)	(13.4)
Principal payments on capital lease obligations			(4.8)	(3.3)
Payment of debt issuance costs			(29.0)	(2.9)
Contributions to parent				(81.1)
Excess tax benefit from stock-based compensation				7.9
Net cash provided by financing activities			1,422.6	302.4
Net cash flows			32.0	(93.4)
Effect of changes in foreign exchange rates on cash			(4.4)	0.1
Net increase/(decrease) in cash and cash equivalents			27.6	(93.3)
Cash and cash equivalents, beginning of period			170.1	308.0
Cash and cash equivalents, end of period	197.7	214.7	197.7	214.7
Zayo Group, LLC [Member]
Net cash provided by operating activities			575.9	464.2
Cash flows from investing activities
Purchases of property and equipment			(573.7)	(475.2)
Acquisitions, net of cash acquired			(1,428.3)	(323.7)
Other			1.5
Net cash used in investing activities			(2,000.5)	(798.9)
Cash flows from financing activities
Proceeds from debt			3,293.8	395.2
Principal payments on long-term debt			(1,837.4)	(13.4)
Principal payments on capital lease obligations			(3.8)	(3.0)
Payment of debt issuance costs			(29.0)	(2.9)
Contributions to parent			10.8	(95.8)
Loan to parent				(99.1)
Receipt from/(payment of) principal balance of intercompany loans			3.6
Excess tax benefit from stock-based compensation				9.0
Net cash provided by financing activities			1,438.0	190.0
Net cash flows			13.4	(144.7)
Effect of changes in foreign exchange rates on cash			(0.1)
Net increase/(decrease) in cash and cash equivalents			13.3	(144.7)
Cash and cash equivalents, beginning of period			91.3	275.9
Cash and cash equivalents, end of period	104.6	131.2	104.6	131.2
Guarantor Subsidiaries [Member]
Net cash provided by operating activities			2.8	1.5
Cash flows from financing activities
Receipt from/(payment of) principal balance of intercompany loans			(3.6)
Excess tax benefit from stock-based compensation				(1.1)
Net cash provided by financing activities			(3.6)	(1.1)
Net cash flows			(0.8)	0.4
Net increase/(decrease) in cash and cash equivalents			(0.8)	0.4
Cash and cash equivalents, beginning of period			3.0	3.1
Cash and cash equivalents, end of period	2.2	3.5	2.2	3.5
Non-Guarantor Subsidiaries [Member]
Net cash provided by operating activities			86.2	72.2
Cash flows from investing activities
Purchases of property and equipment			(56.5)	(41.5)
Acquisitions, net of cash acquired			1.5	(93.3)
Net cash used in investing activities			(55.0)	(134.8)
Cash flows from financing activities
Principal payments on capital lease obligations			(1.0)	(0.3)
Contributions to parent			(10.8)	14.7
Loan to parent				99.1
Net cash provided by financing activities			(11.8)	113.5
Net cash flows			19.4	50.9
Effect of changes in foreign exchange rates on cash			(4.3)	0.1
Net increase/(decrease) in cash and cash equivalents			15.1	51.0
Cash and cash equivalents, beginning of period			75.8	29.0
Cash and cash equivalents, end of period	$ 90.9	$ 80.0	$ 90.9	$ 80.0