Fair Value Disclosures - (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Debt [Details]
Carrying amount of long term debt including current maturities	$ 12,441,000,000		$ 12,441,000,000		$ 12,642,000,000
Fair value of total long term debt including current maturities	13,800,000,000		13,800,000,000		14,000,000,000
Schedule Of Available For Sale Securities [Line Items]
Fair Value	1,698,000,000		1,698,000,000		1,587,000,000
Unrealized Losses	15,000,000		15,000,000		19,000,000
Unrealized Gains	494,000,000		494,000,000		439,000,000
Aggregate fair value of investments related to unrealized losses
Aggregate fair value of investments related to unrealized losses	149,000,000		149,000,000		195,000,000
Fair value of available for sale debt securities by contractual maturity
Due in one year or less	54,000,000		54,000,000
Due after one through five years	132,000,000		132,000,000
Due after five through 10 years	205,000,000		205,000,000
Due after 10 years	68,000,000		68,000,000
Total	459,000,000		459,000,000
Sales of available for sale securities
Proceeds	1,448,000,000	1,755,000,000	3,192,000,000	3,692,000,000
Realized gains	6,000,000	6,000,000	14,000,000	10,000,000
Realized losses	6,000,000	10,000,000	10,000,000	16,000,000
Nuclear decommissioning trust funds
Common stock equity	1,098,000,000		1,098,000,000		1,021,000,000
Preferred stock and other equity	53,000,000		53,000,000		28,000,000
Corporate debt	93,000,000		93,000,000		86,000,000
U.S. state and municipal debt	110,000,000		110,000,000		132,000,000
U.S. and foreign government debt	249,000,000		249,000,000		261,000,000
Money market funds and other	83,000,000		83,000,000		43,000,000
Total nuclear decommissioning trust funds	1,686,000,000		1,686,000,000		1,571,000,000
Derivatives
Commodity forward contracts	18,000,000		18,000,000		15,000,000
Interest rate contracts	1,000,000		1,000,000		4,000,000
Other marketable securities
Corporate debt					4,000,000
U.S. and foreign government debt					3,000,000
Money market and other	28,000,000		28,000,000		18,000,000
Total assets	1,733,000,000		1,733,000,000		1,615,000,000
Derivatives
Commodity forward contracts	412,000,000		412,000,000		494,000,000
Interest rate contracts	35,000,000		35,000,000		39,000,000
Contingent value obligations derivatives	11,000,000		11,000,000		15,000,000
Total liabilities	458,000,000		458,000,000		548,000,000
Fair value hierarchy
Derivatives, net at beginning of period	32,000,000	52,000,000	36,000,000	39,000,000
deferred as regulatory assets and liabilities, net	5,000,000	10,000,000	1,000,000	23,000,000
Derivatives, net at end of period	37,000,000	62,000,000	37,000,000	62,000,000
Common stock equity
Schedule Of Available For Sale Securities [Line Items]
Fair Value	1,098,000,000		1,098,000,000		1,021,000,000
Unrealized Losses	13,000,000		13,000,000		13,000,000
Unrealized Gains	462,000,000		462,000,000		408,000,000
Preferred stock and other equity
Schedule Of Available For Sale Securities [Line Items]
Fair Value	53,000,000		53,000,000		28,000,000
Unrealized Losses	0		0		0
Unrealized Gains	12,000,000		12,000,000		11,000,000
Corporate debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	94,000,000		94,000,000		90,000,000
Unrealized Losses	0		0		0
Unrealized Gains	5,000,000		5,000,000		6,000,000
U.S. state and municipal debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	109,000,000		109,000,000		132,000,000
Unrealized Losses	2,000,000		2,000,000		4,000,000
Unrealized Gains	3,000,000		3,000,000		3,000,000
U.S. and foreign government debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	249,000,000		249,000,000		264,000,000
Unrealized Losses	0		0		2,000,000
Unrealized Gains	11,000,000		11,000,000		10,000,000
Money market funds and other
Schedule Of Available For Sale Securities [Line Items]
Fair Value	95,000,000		95,000,000		52,000,000
Unrealized Losses	0		0		0
Unrealized Gains	1,000,000		1,000,000		1,000,000
Level 1
Nuclear decommissioning trust funds
Common stock equity	1,098,000,000		1,098,000,000		1,021,000,000
Preferred stock and other equity	26,000,000		26,000,000		22,000,000
Corporate debt	0		0		0
U.S. state and municipal debt	0		0		0
U.S. and foreign government debt	100,000,000		100,000,000		79,000,000
Money market funds and other	2,000,000		2,000,000		1,000,000
Total nuclear decommissioning trust funds	1,226,000,000		1,226,000,000		1,123,000,000
Derivatives
Commodity forward contracts	0		0		0
Interest rate contracts	0		0		0
Other marketable securities
Corporate debt					0
U.S. and foreign government debt					0
Money market and other	21,000,000		21,000,000		18,000,000
Total assets	1,247,000,000		1,247,000,000		1,141,000,000
Level 1
Derivatives
Commodity forward contracts	0		0		0
Interest rate contracts	0		0		0
Contingent value obligations derivatives	0		0		0
Total liabilities	0		0		0
Level 2
Nuclear decommissioning trust funds
Common stock equity	0		0		0
Preferred stock and other equity	27,000,000		27,000,000		6,000,000
Corporate debt	93,000,000		93,000,000		86,000,000
U.S. state and municipal debt	110,000,000		110,000,000		132,000,000
U.S. and foreign government debt	149,000,000		149,000,000		182,000,000
Money market funds and other	81,000,000		81,000,000		42,000,000
Total nuclear decommissioning trust funds	460,000,000		460,000,000		448,000,000
Derivatives
Commodity forward contracts	18,000,000		18,000,000		15,000,000
Interest rate contracts	1,000,000		1,000,000		4,000,000
Other marketable securities
Corporate debt					4,000,000
U.S. and foreign government debt					3,000,000
Money market and other	7,000,000		7,000,000		0
Total assets	486,000,000		486,000,000		474,000,000
Level 2
Derivatives
Commodity forward contracts	376,000,000		376,000,000		458,000,000
Interest rate contracts	35,000,000		35,000,000		39,000,000
Contingent value obligations derivatives	11,000,000		11,000,000		15,000,000
Total liabilities	422,000,000		422,000,000		512,000,000
Level 3
Nuclear decommissioning trust funds
Common stock equity	0		0		0
Preferred stock and other equity	0		0		0
Corporate debt	0		0		0
U.S. state and municipal debt	0		0		0
U.S. and foreign government debt	0		0		0
Money market funds and other	0		0		0
Total nuclear decommissioning trust funds	0		0		0
Derivatives
Commodity forward contracts	0		0		0
Interest rate contracts	0		0		0
Other marketable securities
Corporate debt					0
U.S. and foreign government debt					0
Money market and other	0		0		0
Total assets	0		0		0
Level 3
Derivatives
Commodity forward contracts	36,000,000		36,000,000		36,000,000
Interest rate contracts	0		0		0
Contingent value obligations derivatives	0		0		0
Total liabilities	$ 36,000,000		$ 36,000,000		$ 36,000,000