Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 35	$ 38
Interest Cost	42	35
Expected Return on Plan Assets	(121)	(119)
Amortization of Prior Service Cost	0	0
Amortization of Actuarial Loss	15	26
Non-Operating Pension and OPEB (Credits) Costs	(64)	(58)
Total Benefit (Credits) Costs	(29)	(20)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2
Interest Cost	6	5
Expected Return on Plan Assets	(11)	(10)
Amortization of Prior Service Cost	(32)	(32)
Amortization of Actuarial Loss	4	11
Non-Operating Pension and OPEB (Credits) Costs	(33)	(26)
Total Benefit (Credits) Costs	$ (31)	$ (24)