Commitments and Contingencies (Environmental Matters) (Narrative) (Detail) gal in Millions, $ in Millions		1 Months Ended						6 Months Ended
	Oct. 31, 2014 Facility MGD	May 31, 2024 Station	Oct. 31, 2020	Nov. 30, 2019 gal	Sep. 30, 2017 Petition	Apr. 30, 2017 Petition	Aug. 31, 2016 T	Jun. 30, 2025 USD ($) Facility Product Indicator
Loss Contingencies [Line Items]
Measurement of groundwater withdrawals | gal				3
Number of manufacturing gas plant decommissioned sites that contain residues of byproduct chemicals | Product								4
Environmental remediation costs recognized in regulatory assets | $								$ 33
Number of facilities inactive subject to final rule								3
Unfavorable Regulatory Action | CWA
Loss Contingencies [Line Items]
Electric generating stations with water withdrawals with heightened entrainment analysis under CWA | MGD	2
Number of mandatory facility specific factors. | Indicator								5
Number of optional facility specific factors | Indicator								6
Unfavorable Regulatory Action | CWA | DESC
Loss Contingencies [Line Items]
Number of DESC facilities subject to final regulations	5
Maximum [Member]
Loss Contingencies [Line Items]
Estimated environmental remediation activities at manufacturing gas plant sites | $								$ 1
Environmental Protection Agency And State Regulatory Agencies [Member] | Hydroelectric Facilities
Loss Contingencies [Line Items]
Number of DESC hydroelectric facilities subject to regulations	5
EPA
Loss Contingencies [Line Items]
Number of petition agreed for reconsideration | Petition					2
EPA | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Electric generating stations with water withdrawals under CWA | MGD	125
EPA | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Number of separate petitions for reconsideration granted | Petition						2
Loss contingencies facility retirement period		2034
EPA | Minimum [Member] | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies individual facilities circumstances period			2021
EPA | Maximum [Member]
Loss Contingencies [Line Items]
Number of stations inactive subject to final rule | Station		7
EPA | Maximum [Member] | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies individual facilities circumstances period		2029	2028
Carbon Regulations
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T							75,000