Regulatory Matters (Details Textuals) (USD $)	9 Months Ended
	Sep. 30, 2012 Electric Utility [Member] kWh	Sep. 30, 2011 Electric Utility [Member]	Sep. 30, 2011 Gas Utility [Member]	Sep. 30, 2012 Gas Utility [Member] months	Jun. 30, 2012 Gas Utility [Member] months
Regulatory Asset and Liability [Line Items]
Accrued Liabilities for RDM Refunds Relating to 2010	$ 56,000,000
Accrued Liabilities for RDM Refunds Relating to 2011	71,000,000
Defer the Reversal of RDM Liability	127,000,000
Monthly Amount to Amortize from Liability to Income	10,600,000
Requested Recovery of Energy Optimization Expenses for Future Period		224,000,000	66,000,000
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
Gas Rate Increase to Recover Higher Costs				77,000,000
Self Implement Utility Rates				34,000,000
RDM Application Proposed Recovery				8,600,000	20,000,000
Time Period to Implement RDM Surcharge					12
RDM Revenue Recognized For 2010/2011 Period					5,000,000
RDM Revenue Recognized for 2011/2012 Period					3,000,000
GCR Time Period of Reconciliation				12
GCR Reconciliation Over-Recovery				6,000,000
UETM Net Refund				7,000,000
UTEM Sufficiency Gross Amount Related to Uncollectibles				19,000,000
Under Recovery Relating to Under-Collection of UETM Gross				$ 12,000,000
Time Period to Implementation Credits and Surcharges Related to the UETM				12