Utility Regulatory Assets and Liabilities and Regulatory Matters (Details Textuals) (USD $) In Millions	3 Months Ended
	Dec. 31, 2010	Jun. 30, 2011	Jun. 23, 2011	Mar. 31, 2011	Jan. 14, 2011	Sep. 30, 2010	Jun. 30, 2010
Utility regulatory assets and liabilities and regulatory matters [Textuals Abstract]
Gas utility unrealized losses on derivative financial instruments contracts		$ 1.1				$ 1.4	$ 0.6
Decrease in regulatory assets on remeasurement of merged plan's assets and benefit obligations	43.1
Fair values of electric utility's forward purchase power agreements		33.5					60.0
Net book value of storage facility assets				10.9
Expected Increase in base operating revenues by CPG Base Rate Filing					16.5
Increase in distribution rates, Base rate revenue			8.0
Amount included in distribution rates for CPG'S Energy and Efficiency Conservation Program			0.9
Electric Utility - Forward Contract [Member]
Utility regulatory assets and liabilities and regulatory matters [Textuals Abstract]
Fair values of electric utility's forward purchase power agreements		$ 10.1				$ 19.7