Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 29	$ 25	$ 58	$ 50
Interest Cost	53	55	107	111
Expected Return on Plan Assets	(87)	(77)	(174)	(153)
Amortization of Net Transition Obligation	0	0	0	0
Amortization of Prior Service Cost	(4)	(4)	(9)	(9)
Amortization of Actuarial Loss	47	42	94	84
Net Periodic Benefit Cost	38	41	76	83
Effect of Regulatory Asset	0	0	0	0
Total Benefit Costs, Including Effect of Regulatory Asset	38	41	76	83
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	5	4	10	8
Interest Cost	16	16	32	32
Expected Return on Plan Assets	(5)	(5)	(10)	(9)
Amortization of Net Transition Obligation	0	0	0	1
Amortization of Prior Service Cost	(3)	(3)	(7)	(7)
Amortization of Actuarial Loss	10	8	21	16
Net Periodic Benefit Cost	23	20	46	41
Effect of Regulatory Asset	0	5	0	10
Total Benefit Costs, Including Effect of Regulatory Asset	$ 23	$ 25	$ 46	$ 51