Pension, OPEB and Savings Plans (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 101	$ 92	$ 87
Interest Cost	223	228	231
Expected Return on Plan Assets	(306)	(334)	(266)
Amortization of Net Transition Obligation	0	0	0
Amortization of Prior Service Cost	(18)	(11)	0
Amortization of Actuarial Loss	167	119	122
Net Periodic Benefit Cost	167	94	174
Special Termination Benefits	1	0
Effect of Regulatory Asset	0	0
Total Benefit Costs, Including Effect of Regulatory Asset	168	94	174
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	17	14	16
Interest Cost	65	61	72
Expected Return on Plan Assets	(17)	(18)	(14)
Amortization of Net Transition Obligation	2	4	27
Amortization of Prior Service Cost	(14)	(13)	13
Amortization of Actuarial Loss	31	14	8
Net Periodic Benefit Cost	84	62	122
Effect of Regulatory Asset	19	19	19
Total Benefit Costs, Including Effect of Regulatory Asset	$ 103	$ 81	$ 141