Derivative Instruments (Details 4) (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
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Loss) Recognized in OCI (Effective Portion)	$ (48)		$ (48)		$ (48)		$ 58
Gain (Loss) Reclassified from AOCI into Income (EffectivePortion)	4	[1]	31	[1]	14	[1]	(44)	[1]
Gain (Loss) Reclassified from AOCI into Income (IneffectivePortion)	0		0		2		0
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Loss) Recognized in OCI (Effective Portion)	(35)		(9)		(34)		94
Gain (Loss) Reclassified from AOCI into Income (EffectivePortion)	(8)	[1],[2]	(22)	[1],[2]	(15)	[1],[3]	(123)	[1],[3]
Gain (Loss) Reclassified from AOCI into Income (IneffectivePortion)	0		(1)		0		(1)
Commodity Option [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Loss) Recognized in OCI (Effective Portion)	(13)		(39)		(14)		(36)
Gain (Loss) Reclassified from AOCI into Income (EffectivePortion)	12	[1],[4]	53	[1],[4]	29	[1],[4]	79	[1],[4]
Gain (Loss) Reclassified from AOCI into Income (IneffectivePortion)	$ 0		$ 1		$ 2		$ 1

[1] Cumulative cash flow hedge losses, net of tax, remaining in AOCI were $216 million and $172 million at June 30, 2012 and December 31, 2011, respectively.

[2] Reclassification of losses from OCI to earnings consisted of $8 million and $7 million from the reclassification of interest rate contracts due to settlement for the three months ended June 30, 2012 and 2011, respectively, and $15 million in losses from terminated interest rate contracts due to repayment of project debt in June 2011 for the three months ended June 30, 2011

[3] Reclassification of losses from OCI to earnings consisted of $15 million and $17 million from the reclassification of interest rate contracts due to settlement for the six months ended June 30, 2012 and 2011, respectively, $15 million in losses from terminated interest rate contracts due to repayment of project debt in June 2011, and $91 million in losses from existing interest rate contracts reclassified from OCI into earnings due to the refinancing of variable rate First Lien Credit Facility term loans for the six months ended June 30, 2011.

[4] Included in operating revenues and fuel and purchased energy expense on our Consolidated Condensed Statement of Operations.