Retirement Benefits and Trusteed Assets (Details 1) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 395	$ 619
Amortization of net actuarial loss	(178)	(142)
Amortization of prior service cost	0	(3)
Total recognized Regulatory assets and Other comprehensive income	217	474
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive income	437	646
Net actuarial loss	$ 202	$ 171