Retirement Benefits and Trusteed Assets (Pension Plan - Other Changes in Plan Assets and Benefit Obligations recognized in Reg Assets and OCI) (Details) (Pension Plan [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Other changes in plan assets and benefit obligations recognized in Regulatory assets and Other comprehensive income
Net actuarial (gain) loss	$ 614	$ (418)
Amortization of net actuarial loss	(110)	(148)
Prior service cost	(2)	0
Amortization of prior service cost	(2)	(1)
Total recognized in Regulatory assets and Other comprehensive income	500	(567)
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive income	644	(383)
Estimated amounts to be amortized from Regulatory assets and Accumulated other comprehensive income into net periodic benefit cost during next fiscal year
Net actuarial loss	149	106
Prior service cost	$ 1	$ 1