Pension and Other Postretirement Benefits (OPEB) - Schedule of Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost (included in O&M Expense)	$ 22	$ 24	$ 44	$ 47
Interest Cost	58	56	116	112
Expected Return on Plan Assets	(77)	(81)	(154)	(161)
Amortization of Net Prior Service Credit	0	0	0	0
Amortization of Net Actuarial Loss (Gain)	16	18	31	36
Non-Service Components of Pension and OPEB (Credits) Costs	(3)	(7)	(7)	(13)
Total Net Benefit (Credits) Costs	19	17	37	34
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost (included in O&M Expense)	1	0	1	1
Interest Cost	9	10	18	19
Expected Return on Plan Assets	(9)	(8)	(17)	(17)
Amortization of Net Prior Service Credit	0	1	1	1
Amortization of Net Actuarial Loss (Gain)	(1)	(1)	(2)	(1)
Non-Service Components of Pension and OPEB (Credits) Costs	(1)	2	0	2
Total Net Benefit (Credits) Costs	$ 0	$ 2	$ 1	$ 3