Fair Value Disclosures - (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Additional Fair Value Elements [Abstract]
Carrying amount of long term debt including current maturities	$ 12,941,000,000	$ 12,642,000,000
Long-term Debt, Fair Value	15,300,000,000	14,000,000,000
Schedule Of Available For Sale Securities [Line Items]
Fair Value	1,630,000,000	1,587,000,000
Unrealized Losses	31,000,000	19,000,000
Unrealized Gains	444,000,000	439,000,000
Aggregate fair value of investments related to unrealized losses
Aggregate fair value of investments related to unrealized losses	136,000,000	195,000,000
Fair value of available for sale debt securities by contractual maturity
Due in one year or less	44,000,000
Due after one through five years	231,000,000
Due after five through 10 years	147,000,000
Due after 10 years	90,000,000
Total	512,000,000
Sales of available for sale securities
Proceeds	4,640,000,000	6,747,000,000	2,207,000,000
Realized gains	30,000,000	21,000,000	26,000,000
Realized losses	33,000,000	27,000,000	87,000,000
Nuclear decommissioning trust funds
Common stock equity	1,033,000,000	1,021,000,000
Preferred stock and other equity	29,000,000	28,000,000
Corporate debt	86,000,000	86,000,000
U.S. state and municipal debt	128,000,000	132,000,000
U.S. and foreign government debt	284,000,000	261,000,000
Money market funds and other	87,000,000	43,000,000
Total nuclear decommissioning trust funds	1,647,000,000	1,571,000,000
Derivatives
Commodity forward contracts	5,000,000	15,000,000
Interest rate contracts		4,000,000
Other marketable securities
Corporate debt		4,000,000
U.S. and foreign government debt		3,000,000
Money market and other	20,000,000	18,000,000
Total assets	1,672,000,000	1,615,000,000
Derivatives
Commodity forward contracts	692,000,000	494,000,000
Interest rate contracts	93,000,000	39,000,000
Contingent value obligations derivatives	14,000,000	15,000,000
Total liabilities	799,000,000	548,000,000
Fair value hierarchy
Derivatives, net at beginning of period			41,000,000
Level 1
Nuclear decommissioning trust funds
Common stock equity	1,033,000,000	1,021,000,000
Preferred stock and other equity	28,000,000	22,000,000
U.S. and foreign government debt	87,000,000	79,000,000
Money market funds and other		1,000,000
Total nuclear decommissioning trust funds	1,148,000,000	1,123,000,000
Other marketable securities
Money market and other	20,000,000	18,000,000
Total assets	1,168,000,000	1,141,000,000
Level 2
Nuclear decommissioning trust funds
Preferred stock and other equity	1,000,000	6,000,000
Corporate debt	86,000,000	86,000,000
U.S. state and municipal debt	128,000,000	132,000,000
U.S. and foreign government debt	197,000,000	182,000,000
Money market funds and other	87,000,000	42,000,000
Total nuclear decommissioning trust funds	499,000,000	448,000,000
Derivatives
Commodity forward contracts	5,000,000	15,000,000
Interest rate contracts		4,000,000
Other marketable securities
Corporate debt		4,000,000
U.S. and foreign government debt		3,000,000
Total assets	504,000,000	474,000,000
Derivatives
Commodity forward contracts	668,000,000	458,000,000
Interest rate contracts	93,000,000	39,000,000
Contingent value obligations derivatives	14,000,000	15,000,000
Total liabilities	775,000,000	512,000,000
Level 3
Derivatives
Commodity forward contracts	24,000,000	36,000,000
Total liabilities	24,000,000	36,000,000
Fair value hierarchy
Derivatives, net at end of period	24,000,000	36,000,000	39,000,000
Common Stock Outstanding - Amount
Schedule Of Available For Sale Securities [Line Items]
Fair Value	1,033,000,000	1,021,000,000
Unrealized Losses	29,000,000	13,000,000
Unrealized Gains	401,000,000	408,000,000
Preferred stock and other equity
Schedule Of Available For Sale Securities [Line Items]
Fair Value	29,000,000	28,000,000
Unrealized Gains	11,000,000	11,000,000
Corporate debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	86,000,000	90,000,000
Unrealized Gains	6,000,000	6,000,000
U.S. state and municipal debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	128,000,000	132,000,000
Unrealized Losses	2,000,000	4,000,000
Unrealized Gains	7,000,000	3,000,000
U.S. and foreign government debt
Schedule Of Available For Sale Securities [Line Items]
Fair Value	284,000,000	264,000,000
Unrealized Losses		2,000,000
Unrealized Gains	18,000,000	10,000,000
Commodity derivatives | Level 3
Fair value hierarchy
Deferred as regulatory assets and liabilities, net	21,000,000	44,000,000	13,000,000
Transfers in (out) of level 3, net	(33,000,000)	(47,000,000)	(15,000,000)
Money market funds and other securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value	70,000,000	52,000,000
Unrealized Gains	1,000,000	1,000,000
CVOs | Level 3
Fair value hierarchy
Repurchases under settlement and tender offer	(60,000,000)
Transfers into Level 3	74,000,000
Transfers out of Level 3	$ (14,000,000)