Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 13		$ 17		$ 16		$ 17
Included in net income:
Included in operating revenues	3	[1]	(24)	[1]	4	[1]	(17)	[1]
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense	0	[2]	2	[2]	0	[2]	0	[2]
Included in OCI	0		0		0		4
Purchases, issuances and settlements:
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	0		(1)		(1)		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(3)		(5)		(5)		(11)
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
Transfers into level 3	0	[3]	0	[3]	0	[3]	0	[3]
Transfers out of Level 3	1	[4]	0	[4]	2	[4]	3	[4]
Balance, end of period	13		(10)		13		(10)
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Change in Unrealized Gain (Loss) Held At Period End	3		(22)		4		(17)
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure	699				699				1,274
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure	$ 172				$ 172				$ 228

[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 each of the three and six months ended June 30, 2013 and 2012.

[4] We had $1 million in gains transferred out of level 3 into level 2 for the three months ended June 30, 2013 and $2 million and $3 million in gains transferred out of level 3 into level 2 for the six months ended June 30, 2013 and 2012, respectively, due to changes in market liquidity in various power markets. There were no transfers out of level 3 into level 2 for the three months ended June 30, 2012.