Employee Benefit Plans (AOCI and Regulatory Assets and Liabilities that have Not been Recognized as Components of Periodic Benefit (Credit) Cost) (Parenthetical) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Assets and Liabilities Held for Sale
Defined Benefit Plan Disclosure [Line Items]
Amount included in AOCI		$ 173	$ 170
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	3,023	2,717
Amount included in AOCI		1,800	1,700
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	(156)	(73)
Amount included in AOCI		$ (38)	$ 14

[1] As of December 31, 2023, of the $3.0 billion and $(156) million related to pension benefits and other postretirement benefits, $1.8 billion and $(38) million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities, except for $173 million presented in assets and liabilities held for sale. As of December 31, 2022, of the $2.7 billion and $(73) million related to pension benefits and other postretirement benefits, $1.7 billion and $14 million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities, except for $170 million presented in assets and liabilities held for sale.