Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 30	$ 26	$ 92	$ 78
Interest Cost	59	58	176	176
Expected Return on Plan Assets	(103)	(99)	(310)	(299)
Amortization of Prior Service Cost	(5)	(5)	(14)	(14)
Amortization of Actuarial Loss	38	14	112	42
Total Benefit Costs	19	(6)	56	(17)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	5	5	16	14
Interest Cost	16	18	50	52
Expected Return on Plan Assets	(7)	(7)	(22)	(20)
Amortization of Prior Service Cost	(4)	(4)	(11)	(11)
Amortization of Actuarial Loss	11	6	32	18
Total Benefit Costs	$ 21	$ 18	$ 65	$ 53