Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 27	$ 31	$ 54	$ 62
Interest Cost	51	58	101	117
Expected Return on Plan Assets	(99)	(104)	(197)	(207)
Amortization of Prior Service Cost	(5)	(4)	(9)	(9)
Amortization of Actuarial Loss	40	37	79	74
Total Benefit Costs	14	18	28	37
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	4	6	8	11
Interest Cost	14	17	29	34
Expected Return on Plan Assets	(7)	(8)	(15)	(15)
Amortization of Prior Service Cost	(4)	(4)	(7)	(7)
Amortization of Actuarial Loss	10	11	20	21
Total Benefit Costs	$ 17	$ 22	$ 35	$ 44