Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified				9 Months Ended
	Dec. 31, 2010 Antargaz Competition Authority [Member]	Jun. 30, 2011 Environmental matters [Member]	Jun. 30, 2011 SCE&G [Member]	Jun. 30, 2011 KeySpan [Member]	Jun. 30, 2011 Northeast Companies [Member]
Commitments and Contingencies (Textuals) [Abstract]
Litigating claims relating to sites		2
Alleged percentage of liability for MGP site			25.00%
Approximate remediation cost spent by claimant			$ 22.0	$ 2.3
Approximate third party claim paid by claimant			26
Environmental Exit Cost Anticipated by Claimant			14	11	25
Alleged percentage of responsibility for cost by claimant				50.00%
Environmental Exit Cost Based on Third Party Estimate				10
Additional Environment Exit Cost Based On Claimant Estimate				20
Reversal of Competition Authority Matter Accrual	$ 9.4