Retirement Benefits (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Amounts recognized in the consolidated balance sheets related to company's pension plans
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 OCI	(111,000,000)	(70,000,000)
Other Postretirement Benefits [Member]
Changes in the accumulated postretirement benefit obligations (APBO) and in fair value of plan assets
Benefit obligation at beginning of year	1,752,000,000	1,759,000,000
Service cost	21,000,000	25,000,000	26,000,000
Interest cost	92,000,000	100,000,000	113,000,000
Benefits paid	(103,000,000)	(95,000,000)
Actuarial loss (gain)	29,000,000	(41,000,000)
Plan amendments	12,000,000	2,000,000
Retiree drug subsidy	8,000,000	6,000,000
Balance at end of year	1,787,000,000	1,752,000,000	1,759,000,000
Fair value of plan assets at beginning of year	802,000,000	743,000,000
Actual return (loss) on plan assets	4,000,000	82,000,000
Employer contributions	54,000,000	66,000,000
Benefits paid	(95,000,000)	(89,000,000)
Fair value of plan assets at end of year	765,000,000	802,000,000	743,000,000
Accrued liability	(1,022,000,000)	(950,000,000)
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	345,000,000	292,000,000
Other current liabilities	(4,000,000)	(1,000,000)
Employee benefit obligations	(1,018,000,000)	(949,000,000)
Accumulated OCI	$ 6,000,000	$ 3,000,000