Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 28	$ 30	$ 82	$ 92
Interest Cost	50	59	151	176
Expected Return on Plan Assets	(98)	(103)	(295)	(310)
Amortization of Prior Service Cost	(5)	(5)	(14)	(14)
Amortization of Actuarial Loss	39	38	118	112
Total Benefit Costs	14	19	42	56
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	5	5	13	16
Interest Cost	15	16	44	50
Expected Return on Plan Assets	(8)	(7)	(23)	(22)
Amortization of Prior Service Cost	(4)	(4)	(11)	(11)
Amortization of Actuarial Loss	10	11	30	32
Total Benefit Costs	$ 18	$ 21	$ 53	$ 65