Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 23	$ 22
Interest Cost	56	69
Expected Return on Plan Assets	(80)	(95)
Amortization of Prior Service Cost	0	0
Amortization of Actuarial Loss	18	24
Non-Operating Pension and OPEB (Credits) Costs	(6)	(2)
Total Benefit (Credits) Costs	17	20
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1	1
Interest Cost	9	10
Expected Return on Plan Assets	(9)	(8)
Amortization of Prior Service Cost	0	(13)
Amortization of Actuarial Loss	0	(1)
Non-Operating Pension and OPEB (Credits) Costs	0	(12)
Total Benefit (Credits) Costs	$ 1	$ (11)