Retirement Benefits and Trusteed Assets (Details 1) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 619	$ 166
Amortization of net actuarial loss	(142)	(100)
Amortization of prior service cost	(3)	(4)
Total recognized Regulatory assets and Other comprehensive income	474	62
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive income	646	174
Net actuarial loss	171	133
Prior service credit	$ 0	$ 3