Pension and Other Postretirement Benefits (OPEB) - Schedule of Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Pension Lift Out Settlement Charge		$ 332
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost (included in O&M Expense)	$ 24	23	$ 71	$ 68
Interest Cost	57	62	169	200
Expected Return on Plan Assets	(80)	(87)	(241)	(278)
Amortization of Prior Service Credit	0	0	0	0
Amortization of Actuarial Loss (Gain)	17	19	53	67
Pension Lift Out Settlement Charge	0	332	0	332
Non-Service Components of Pension and OPEB (Credits) Costs	(6)	326	(19)	321
Total Net Benefit (Credits) Costs	18	349	52	389
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost (included in O&M Expense)	1	1	2	3
Interest Cost	9	10	28	31
Expected Return on Plan Assets	(9)	(8)	(26)	(25)
Amortization of Prior Service Credit	0	(13)	1	(39)
Amortization of Actuarial Loss (Gain)	0	(1)	(1)	(2)
Pension Lift Out Settlement Charge	0	0	0	0
Non-Service Components of Pension and OPEB (Credits) Costs	0	(12)	2	(35)
Total Net Benefit (Credits) Costs	$ 1	$ (11)	$ 4	$ (32)