Employee Benefit Plans (AOCI and Regulatory Assets and Liabilities that have Not been Recognized as Components of Periodic Benefit (Credit) Cost) (Detail) - USD ($) $ in Millions		Dec. 31, 2024	Dec. 31, 2023
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets and liabilities, net actuarial loss (gain)	[1]	$ 496	$ 1,237
Regulatory assets and liabilities, prior service cost (credit)	[1]	8	2
AOCI, prior service cost (credit)		2	3
Total		506	1,242
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets and liabilities, net actuarial loss (gain)	[1]	(65)	(56)
Regulatory assets and liabilities, prior service cost (credit)	[1]	(41)	(61)
AOCI, prior service cost (credit)		(40)	(60)
Total		$ (146)	$ (177)

[1] At December 31, 2023, includes $173 million presented in assets and liabilities held for sale.