EMPLOYEE BENEFITS (Changes in Benefit Obligations, Fair Value of Plan Assets and Unfunded Status) (Details) $ in Millions, $ in Millions			12 Months Ended
	Oct. 31, 2017 CAD ($)	Oct. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year			$ 93.5
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Fair value of plan assets			93.5	$ 93.5
Allstream
Defined Benefit Plan Disclosure [Line Items]
Assets transferred resulting from Allstream acquisition	$ 117.9	$ 91.6
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year			6.7
Service cost			2.7
Interest cost			2.5
Actuarial loss (gain)			9.3
Participant contributions			0.6
Benefits paid from plan assets			(3.3)
Acquisition transfer			97.6
Settlements			(2.5)
Foreign currency exchange rate changes			(0.1)
Projected benefit obligation at end of year			113.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year			3.7
Acquisition transfer			89.8
Return on plan assets			2.4
Employer contributions			2.9
Participant contributions			0.6
Benefits paid from plan assets			(3.3)
Settlements			(2.6)
Fair value of plan assets at end of year			93.5
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Projected benefit obligation			6.7	113.5
Fair value of plan assets			3.7	93.5
Unfunded status				20.0
Non-current portion of unfunded status				20.0
OPEB Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year			9.9
Service cost			0.1
Interest cost			0.3
Actuarial loss (gain)			0.4
Benefits paid from plan assets			(0.6)
Foreign currency exchange rate changes			(0.1)
Projected benefit obligation at end of year			10.0
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Projected benefit obligation			$ 9.9	$ 10.0