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, 2011	Dec. 31, 2010
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 195	$ 93
Amortization of net actuarial loss	(55)	(54)
Prior service credit	(4)	(79)
Amortization of prior service cost	26	4
Amortization of transition asset	(2)	(2)
Total recognized Regulatory assets and Other comprehensive income	160	(38)
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive icnome	282	126
Net actuarial loss	78	59
Prior service credit	(27)	(26)
Net transition obligation	$ 2	$ 2