Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 17		$ 12		$ 17		$ 30
Included in net income:
Included in operating revenues	(24)	[1]	10	[1]	(17)	[1]	6	[1]
Included in fuel and purchased energy expense	2	[2]	1	[2]	0	[2]	0	[2]
Included in OCI	0		4		4		5
Purchases, issuances and settlements:
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	0		0		0		0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	1		1		1		1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issues	(1)		0		(1)		0
Settlements	(5)		(7)		(11)		(21)
Transfers into level 3	0	[3]	0	[3]	0	[3]	0	[3]
Transfers out of level 3	0	[4]	0	[4]	(3)	[4]	0	[4]
Balance, end of period	(10)		21		(10)		21
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Change in Unrealized Gain (Loss) Held At Period End	(22)		11		(17)		7
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure	574				574				1,249
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure	$ 149				$ 149				$ 166

[1] For power contracts and Heat Rate swaps and options, included on our Consolidated Condensed Statements of Operations.

[2] For natural gas contracts, swaps and options, included on our Consolidated Condensed Statements of Operations.

[3] There were no transfers out of level 2 into level 3 for the three and six months ended June 30, 2012 and 2011.

[4] We had $3 million of transfers out of level 3 into level 2 for the six months ended June 30, 2012. There were no transfers out of level 3 for the three months ended June 30, 2012 and for the three and six months ended June 30, 2011.