Retirement Benefits and Trusteed Assets (Details 9) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Defined Benefit Plans, Liabilities	$ (1,162)	$ (1,485)
Net actuarial loss	(34)	195
Amortization of net actuarial loss	(80)	(55)
Prior service credit	(264)	(4)
Amortization of prior service cost	27	26
Amortization of transition asset	(2)	(2)
Total recognized Regulatory assets and Other comprehensive income	(353)	160
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive icnome	(202)	282
Net actuarial loss	69	78
Prior service credit	(91)	(27)
Net transition obligation	$ 0	$ 2