Retirement Benefits (Details 4) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid Pension Costs	$ 0	$ 88,000,000
Other regulatory assets, deferred	3,532,000,000	2,402,000,000
Other current liabilities	(426,000,000)	(535,000,000)
Employee benefit obligations	(2,442,000,000)	(1,580,000,000)
Accumulated other comprehensive loss	111,000,000	70,000,000
Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid Pension Costs	0	88,000,000
Other regulatory assets, deferred	2,614,000,000	1,749,000,000
Other current liabilities	(34,000,000)	(28,000,000)
Employee benefit obligations	(1,245,000,000)	(449,000,000)
Accumulated other comprehensive loss	109,000,000	68,000,000
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	135,000,000	167,000,000
Net (Gain) Loss	2,588,000,000	1,650,000,000
Prior Service Cost, Estimated	30,000,000
Net (Gain) Loss, Estimated	95,000,000
Pension Plans [Member] | Accumulated Other Comprehensive Income [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	7,000,000	8,000,000
Net (Gain) Loss	102,000,000	60,000,000
Prior Service Cost, Estimated	1,000,000
Net (Gain) Loss, Estimated	4,000,000
Pension Plans [Member] | Regulatory Assets [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	128,000,000	159,000,000
Net (Gain) Loss	2,486,000,000	1,590,000,000
Prior Service Cost, Estimated	29,000,000
Net (Gain) Loss, Estimated	$ 91,000,000