Financial and Other Derivative Instruments (Details Textuals) (USD $)			3 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 FTR [Member]	Sep. 30, 2013 FTR [Member]
Derivative [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 1,000,000
Letters of Credit Outstanding, Amount	21,000,000	63,000,000
Cash Collateral Posted Net of Cash Collateral Received	30,000,000
Collateral Already Posted, Aggregate Fair Value		20,000,000
Cash Collateral Paid or Received for Derivative Assets	29,000,000	0
Cash Collateral Paid or Received for Derivative Liabilities	20,000,000
Cash Collateral Received	24,000,000	24,000,000
Cash Collateral Paid	3,000,000	4,000,000
Effect of Derivative Instruments Recoverable Through PSCR Mechanism			3,000,000	7,000,000
Value of Transactions Company Would Have Been Exposed to if Credit Rating Below Investment Grade	$ 327,000,000