LONG-TERM DEBT (Narrative) (Details) - USD ($) $ in Millions												1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 26, 2018	Dec. 22, 2017	Jul. 20, 2017	Jul. 05, 2017	Apr. 10, 2017	Jan. 27, 2017	Jan. 19, 2017	Jul. 22, 2016	Apr. 14, 2016	Jan. 15, 2016	May 06, 2015	Jul. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Apr. 03, 2019	Jun. 30, 2018	Mar. 09, 2015	Jan. 23, 2015
Debt Instrument [Line Items]
Interest rate decrease (basis points)		(1.00%)
Payment of debt extinguishment costs																$ 4.9
Debt obligations													$ 5,909.3		$ 5,909.3			$ 5,743.1
Proceeds from issuance of private placement				$ 310.7											275.0	462.8
Repayment of debt															$ 108.8	314.4
Loss on extinguishment of debt																4.9
Secured debt ratio													4.50		4.50
Unamortized debt issuance cost due to previous indebtedness													$ 52.2		$ 52.2			59.6
Debt issuance costs													114.1		114.1
Accumulated amortization													61.9		61.9			$ 54.5
Interest expense associated with the amortization of debt issuance costs													$ 2.5	$ 2.4	$ 7.4	$ 7.1
Revolving Credit Facility
Debt Instrument [Line Items]
Weighted average interest rate													4.20%		4.20%			3.80%
Proceeds from revolving credit facility													$ 25.0		$ 275.0
Outstanding letters of credit													170.0		170.0
Outstanding letters of credit increased		$ 50.0
Letters of Credit [Member]
Debt Instrument [Line Items]
Percentage fee on unused capacity		0.25%
Outstanding letters of credit													8.5		8.5
Secured Debt [Member] | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility maximum borrowing capacity											$ 450.0
Remaining borrowing capacity													$ 271.5		$ 271.5
Percentage of excess revolver committed to debt payments															35.00%
Secured debt ratio													5.25		5.25
Term Loan Facility [Member]
Debt Instrument [Line Items]
Quarterly principal payments per quarter, in basis points											0.25%
Interest rate decrease (basis points)								(0.75%)
Percentage of excess cash flows committed to debt payments											50.00%
Weighted average interest rate													4.70%		4.70%			4.30%
Debt obligations							$ 2,500.0
Repriced percentage							99.75%
Repayment of debt									$ 196.0
Term Loan Facility [Member] | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate principal amount outstanding													$ 1,759.3		$ 1,759.3
Debt obligations													$ 170.0		$ 170.0
Incremental Term Loan [Member]
Debt Instrument [Line Items]
Line of credit facility maximum borrowing capacity	$ 150.0									$ 400.0
Priced percent of additional line of credit										99.00%
Debt obligations							$ 1,850.0
Repriced percentage							99.75%
Incremental Term Loan [Member] | Electric Lightwave
Debt Instrument [Line Items]
Interest rate decrease (basis points)			(0.25%)
Maturity period from incurrence							7 years
Debt obligations							$ 650.0
Minimum | Revolving Credit Facility
Debt Instrument [Line Items]
Percentage fee on unused capacity		0.25%
Maximum
Debt Instrument [Line Items]
Total indebtedness ratio													6.00		6.00
Maximum | Revolving Credit Facility
Debt Instrument [Line Items]
Percentage fee on unused capacity		0.375%
Tranche One [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt obligations																	$ 500.0
Tranche One [Member] | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Interest rate decrease (basis points)							(0.75%)
Maturity period from incurrence							4 years
Debt obligations	$ 150.0						$ 500.0
Tranche Two (B-2 Term Loan) [Member]
Debt Instrument [Line Items]
Repayment of debt												$ 310.7
Tranche Two (B-2 Term Loan) [Member] | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Interest rate decrease (basis points)							(0.25%)
Maturity period from incurrence							7 years
Debt obligations							$ 1,350.0
Repayment of debt					$ 570.1
6.00% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Debt obligations													$ 1,430.0		$ 1,430.0			$ 1,430.0
Interest rate of debt redeemed													6.00%		6.00%
6.00% Senior Notes due 2023 [Member] | Unsecured Notes [Member] | Zayo Group Ltd (ZGL) [Member]
Debt Instrument [Line Items]
Debt obligations																				$ 700.0
6.00% Senior Notes due 2023 [Member] | Unsecured Notes [Member] | Zayo Capital [Member]
Debt Instrument [Line Items]
Debt obligations																			$ 730.0
6.375% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Debt obligations													$ 900.0		$ 900.0			900.0
Interest rate of debt redeemed													6.375%		6.375%
6.375% Senior Notes due 2025 [Member] | Unsecured Notes [Member] | Zayo Group Ltd (ZGL) and Zayo Capital [Member]
Debt Instrument [Line Items]
Debt obligations											$ 350.0
Incremental 2025 Notes [Member]
Debt Instrument [Line Items]
Repriced percentage									97.76%
Incremental 2025 Notes [Member] | Unsecured Notes [Member] | Zayo Group Ltd (ZGL) and Zayo Capital [Member]
Debt Instrument [Line Items]
Debt obligations									$ 550.0
5.75% Senior Unsecured Notes due 2027 [Member]
Debt Instrument [Line Items]
Debt obligations				$ 300.0	$ 550.0	$ 800.0							$ 1,650.0		$ 1,650.0			$ 1,650.0
Debt price percentage				104.25%		104.00%
Interest rate of debt redeemed													5.75%		5.75%
10.125% Senior Notes due 2020 [Member]
Debt Instrument [Line Items]
Repayment of debt									325.6
Redemption premium and accrued interest included in redemption amount									$ 20.3
Interest rate of debt redeemed									10.125%
LIBOR [Member] | Term Loan Facility [Member]
Debt Instrument [Line Items]
Spread on interest rate								2.75%
LIBOR [Member] | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate										3.50%
LIBOR [Member] | Incremental Term Loan [Member] | Electric Lightwave
Debt Instrument [Line Items]
Spread on interest rate			2.25%				2.50%
LIBOR [Member] | Minimum | Letters of Credit [Member]
Debt Instrument [Line Items]
Fee on outstanding letters of credit based upon leverage ratio		1.00%
LIBOR [Member] | Minimum | Term Loan Facility [Member]
Debt Instrument [Line Items]
Spread on interest rate		1.00%						1.00%
LIBOR [Member] | Minimum | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate										1.00%
LIBOR [Member] | Minimum | Incremental Term Loan [Member] | Electric Lightwave
Debt Instrument [Line Items]
Spread on interest rate			1.00%				1.00%
LIBOR [Member] | Maximum | Letters of Credit [Member]
Debt Instrument [Line Items]
Fee on outstanding letters of credit based upon leverage ratio		1.75%
LIBOR [Member] | Maximum | Term Loan Facility [Member]
Debt Instrument [Line Items]
Spread on interest rate		1.75%
LIBOR [Member] | Tranche One [Member] | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate	2.25%						2.00%
LIBOR [Member] | Tranche One [Member] | Minimum | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate	1.00%						0.00%
LIBOR [Member] | Tranche Two (B-2 Term Loan) [Member] | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate							2.50%
LIBOR [Member] | Tranche Two (B-2 Term Loan) [Member] | Minimum | Incremental Term Loan [Member]
Debt Instrument [Line Items]
Spread on interest rate							1.00%