Regulatory Matters (Details Textuals) (USD $)	9 Months Ended
	Sep. 30, 2012 kWh
Regulatory Liabilities [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 Enery Optimization Expenses for Future Period	224,000,000
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