Property, Plant and Equipment (Narrative) (Detail) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2024 USD ($) a mi MW	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges		$ 67	$ 37		$ 97	$ 135
Level 3 | Corporate Office Building
Property, Plant and Equipment [Line Items]
Long-lived assets, estimated fair value		23		$ 35	23
Level 3 | Nonregulated renewable natural gas facilities | Minimum
Property, Plant and Equipment [Line Items]
Long-lived assets, estimated fair value		1			$ 1
Impairment of Assets and Other Charges | Corporate Office Building
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges		17		91
Asset impairment charges after tax		12		$ 68
Impairment of Assets and Other Charges | Nonregulated renewable natural gas facilities
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges		33
Asset impairment charges after tax		$ 25
Acquisition of Wind Project | Subsequent Event
Property, Plant and Equipment [Line Items]
Offshore wind project price expected	$ 160
Acquisition of Solar Project Foxhound Virginia
Property, Plant and Equipment [Line Items]
Date Agreement Entered					2023-03
Date Agreement Closed					February 2024
Date of Commercial Operations					April 2024
Acquisition Of Offshore Wind Project
Property, Plant and Equipment [Line Items]
Date Agreement Entered					2024-07
Acquisition Of Offshore Wind Project | Subsequent Event
Property, Plant and Equipment [Line Items]
Miles of area acquired | mi	27
Acres of area acquired | a	40,000
Power generating capacity | MW	800