Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 33	$ 32	$ 90	$ 97
Interest Cost	51	52	167	156
Expected Return on Plan Assets	(108)	(111)	(301)	(331)
Amortization of Prior Service Cost	(4)	(4)	(13)	(13)
Amortization of Actuarial Loss	21	22	75	64
Non-Operating Pension and OPEB (Credits) Costs	(40)	(41)	(72)	(124)
Total Benefit Costs	(7)	(9)	18	(27)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	4	7	13
Interest Cost	12	16	34	49
Expected Return on Plan Assets	(9)	(9)	(27)	(30)
Amortization of Prior Service Cost	(32)	(1)	(96)	(1)
Amortization of Actuarial Loss	13	16	38	48
Non-Operating Pension and OPEB (Credits) Costs	(16)	22	(51)	66
Total Benefit Costs	$ (14)	$ 26	$ (44)	$ 79