Regulatory Matters (Details Textuals) (USD $)	3 Months Ended	12 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012 people	Dec. 31, 2011	Mar. 31, 2012 Electric [Member]	Mar. 31, 2011 Electric [Member]	Sep. 30, 2012 Electric [Member] kWh	Sep. 30, 2011 Electric [Member]	Dec. 31, 2012 Electric [Member]	Jun. 30, 2012 Electric [Member]
Regulatory Asset and Liability [Line Items]
Probability of Recovery Through Regulatory Rates for Regulatory Assets and Liabilities		$ 0
Time Period Required by Non-Bypassable Securitization Bond Surcharge to Recover Securitized Regulatory Asset		14 years
Amortization Period of Cost to Achieve Deferral		10 years
Amortization Period for Enterprise Business Systems		10 years
Approved Rate Base Relating to the AMI Program									37,000,000
Expenditures Net of Grant Funds for AMI Program									110,000,000
Matching Grant Funds for the AMI Program									60,000,000
Defer the Reversal of RDM Liability						127,000,000
Number of Parties that Appealed the COA Decision Regarding RDM		0
Monthly Amount to Amortize from Liability to Income						10,600,000
EO Plans Performance Incentive Surcharges								8,400,000
Requested Recovery of Enery Optimization Expenses for Future Period Revised							224,000,000
Requested net recovery of RETM and LCT			44,000,000
Requesting Authority to Refund Uncollectible Expense to Customers	9,000,000
Authorized Recovery Amount for CIM								63,000,000
Authorized Recovery Period for CIM								10 months
PSCR Reconciliation Calculating net Under Recovery				148,000,000
Net Under Recovery of Power Suppy Cost Recovery Expense					52,600,000
PSCR Reconciliation Includes an Over-Recovery				3,800,000
Net Over Recovery of Power Supply Cost Recovery Expense							10,500,000
Power Supply Cost Recovery Plan Case Factor Next Year						4.74
Total PSCR Forecasted Expense						1,500,000,000
Recovery of Current Year PSCR						$ 81,000,000