Intangible Assets (Schedule of Identifiable Acquisition Related Intangible Assets) (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount	$ 1,079.8	$ 1,082.2
Accumulated Amortization	(175.3)	(155.3)
Total Net	904.5	926.9
Intangible Assets, Gross (Excluding Goodwill)	1,100.6	1,103.6
Intangible Assets, Net	925.3	948.3
Certifications [Member]
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount, Indefinite-lived Intangibles	3.5	3.5
Easement indefinite [Member]
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount, Indefinite-lived Intangibles	17.3	17.9
Customer relationships [Member]
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount	1,077.9	1,080.3
Accumulated Amortization	(174.9)	(155.0)
Total Net	903.0	925.3
Trade names [Member]
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount	0.2	0.2
Accumulated Amortization	(0.1)	(0.1)
Total Net	0.1	0.1
Underlying rights [Member]
Schedule Of Intangible Assets Net Excluding Goodwill [Line Items]
Gross Carrying Amount	1.7	1.7
Accumulated Amortization	(0.3)	(0.2)
Total Net	$ 1.4	$ 1.5