Regulatory Matters (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended	6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended
	Dec. 31, 2011	Jun. 30, 2012 Electric Utility [Member]	Sep. 30, 2011 Electric Utility [Member]	Jun. 30, 2012 Gas Utility [Member] years months	Sep. 30, 2011 Gas Utility [Member]
Regulatory Asset and Liability [Line Items]
Accrued Liabilities for RDM Refunds Relating to 2010		$ 56
Accrued Liabilities for RDM Refunds Relating to 2011		71
Approved Rate Base Relating to the AMI Program		37
Expenditures Net of Grant Funds for AMI Program		90
Matching Grant Funds for the AMI Program		58
RDM Refund Range Minimum First Pilot		56
RDM Refund Range Maximum First Pilot		140
RDM Refund Range Minimum Second Pilot		10
RDM Refund Range Maximum Second Pilot		130
Requested Recovery of Energy Optimization Expenses for Future Period			294		103
EO Plan Expense Cummulative Over Recovery		23		11
Vulnerable Household Warmth Fund Amount to be Collected	48
Customer Monthly Credits to Remove Annualized Funding for VHWF from Rates		40		5
Gas Rate Increase to Recover Higher Costs				77
Annual Incremental Infrastructure Recovery Mechanism to Recover Costs Associated with Capital Investment				5
RDM Application Proposed Recovery				20
Time Period to Implement RDM Surcharge				12
RDM Revenue Recognized For 2010/2011 Period				5
RDM Revenue Recognized for 2011/2012 Period				3
Annual Depreciation Expense Increase				12.4
GCR Time Period of Reconciliation				12
GCR Reconciliation Under-Recovery				6.4
GCR Reconciliation Over-Recovery				$ 1