Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 35	$ 28	$ 70	$ 57
Interest Cost	48	58	96	116
Expected Return on Plan Assets	(110)	(96)	(221)	(193)
Amortization of Prior Service Cost	(3)	(4)	(5)	(9)
Amortization of Actuarial Loss	23	27	46	54
Non-Operating Pension and OPEB (Credits) Costs	(42)	(15)	(84)	(32)
Total Benefit Costs	(7)	13	(14)	25
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	3	5	5
Interest Cost	8	11	17	22
Expected Return on Plan Assets	(9)	(9)	(19)	(18)
Amortization of Prior Service Cost	(32)	(32)	(64)	(64)
Amortization of Actuarial Loss	11	12	23	25
Non-Operating Pension and OPEB (Credits) Costs	(22)	(18)	(43)	(35)
Total Benefit Costs	$ (19)	$ (15)	$ (38)	$ (30)