Pension, OPEB and Savings Plans (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension Lift Out Settlement Charge	$ 6	$ 332	$ 334
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost			90	$ 142	$ 151
Interest Cost			259	167	140
Expected Return on Plan Assets			(361)	(484)	(476)
Amortization of Prior Service Cost			0	0	0
Amortization of Net Actuarial Gain (Loss)			83	60	103
Non-Operating Pension and Other Postretirement Plan (Credits) Costs			319	(257)	(233)
Pension Lift Out Settlement Charge			338	0	0
Net Periodic Benefit Cost			409	(115)	(82)
Total Benefit Costs, Including Effect of Regulatory Asset			409	(115)	(82)
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost			3	6	9
Interest Cost			41	26	22
Expected Return on Plan Assets			(33)	(42)	(42)
Amortization of Prior Service Cost			(52)	(129)	(129)
Amortization of Net Actuarial Gain (Loss)			(2)	15	44
Non-Operating Pension and Other Postretirement Plan (Credits) Costs			(46)	(130)	(105)
Pension Lift Out Settlement Charge			0	0	0
Net Periodic Benefit Cost			(43)	(124)	(96)
Total Benefit Costs, Including Effect of Regulatory Asset			$ (43)	$ (124)	$ (96)