Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 25	$ 23	$ 50	$ 47
Interest Cost	55	58	111	116
Expected Return on Plan Assets	(77)	(82)	(153)	(163)
Amortization of Net Transition Obligation	0	0	0	0
Amortization of Prior Service Cost	(4)	(2)	(9)	(2)
Amortization of Actuarial Loss	42	30	84	60
Net Periodic Benefit Cost	41	27	83	58
Effect of Regulatory Asset	0	0	0	0
Total Benefit Costs, Including Effect of Regulatory Asset	41	27	83	58
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	4	3	8	7
Interest Cost	16	15	32	30
Expected Return on Plan Assets	(5)	(4)	(9)	(8)
Amortization of Net Transition Obligation	0	1	1	3
Amortization of Prior Service Cost	(3)	(3)	(7)	(6)
Amortization of Actuarial Loss	8	4	16	7
Net Periodic Benefit Cost	20	16	41	33
Effect of Regulatory Asset	5	5	10	10
Total Benefit Costs, Including Effect of Regulatory Asset	$ 25	$ 21	$ 51	$ 43