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]
Net actuarial loss	$ (14)	$ 139
Amortization of net actuarial loss	(58)	(40)
Prior service credit	(207)	(3)
Amortization of prior service cost	16	15
Amortization of transition (asset)	(2)	(2)
Total recognized Regulatory assets and Other comprehensive income	(265)	109
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive icnome	(140)	214
Net actuarial loss	50	55
Prior service credit	(69)	(16)
Net transition obligation	$ 0	$ 2