Retirement Benefits and Trusteed Assets (Details 2) (USD $) In Millions, unless otherwise specified	1 Months Ended		12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Regulatory Assets			$ 4,417	$ 4,853
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Accumulated benefit obligation, end of year			4,349	3,881
Benefit obligation, beginning of year	4,195	3,785	4,195	3,785
Service cost			82	69	64
Interest cost			204	202	202
Actuarial loss			474	355
Special termination benefits			2	2	0
Benefits paid			(228)	(218)
Benefit obligation, end of year			4,729	4,195	3,785
Plan assets at fair value, beginning of the year	2,886	2,913	2,886	2,913
Actual return on plan assets			325	(18)
Company contributions	315	229	240	209
Plan assets at fair value, end of the year			3,223	2,886	2,913
Funded status of the plans			(1,506)	(1,309)
Current liabilities			(8)	(11)
Noncurrent liabilities			(1,498)	(1,298)
Pension and Other Postretirement Defined Benefit Plans, Liabilities			(1,506)	(1,309)
Net actuarial loss			205	202
Prior serice cost (credit)			(2)	(3)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax			203	199
Net actuarial loss			2,413	2,201
Prior service cost			7	7
Regulatory Assets			$ 2,420	$ 2,208