Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 29	$ 26	$ 87	$ 76
Interest Cost	54	56	161	167
Expected Return on Plan Assets	(87)	(76)	(261)	(229)
Amortization of Net Transition Obligation	0	0	0	0
Amortization of Prior Service Cost	(5)	(5)	(14)	(14)
Amortization of Actuarial Loss	47	41	141	125
Net Periodic Benefit Cost	38	42	114	125
Defined Benefit Plan, Cost of Providing Special or Contractual Termination Benefits Recognized During Period	0	1	0	1
Effect of Regulatory Asset	0	0	0	0
Total Benefit Costs, Including Effect of Regulatory Asset	38	43	114	126
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	6	5	16	13
Interest Cost	15	17	47	49
Expected Return on Plan Assets	(6)	(4)	(16)	(13)
Amortization of Net Transition Obligation	0	1	0	2
Amortization of Prior Service Cost	(4)	(4)	(11)	(11)
Amortization of Actuarial Loss	11	7	32	23
Net Periodic Benefit Cost	22	22	68	63
Defined Benefit Plan, Cost of Providing Special or Contractual Termination Benefits Recognized During Period	0	0	0	0
Effect of Regulatory Asset	0	4	0	14
Total Benefit Costs, Including Effect of Regulatory Asset	$ 22	$ 26	$ 68	$ 77