Commitments and Contingencies (Environmental Matters) (Narrative) (Detail) $ in Millions		1 Months Ended					12 Months Ended
	Oct. 31, 2014 Facility MGD	Oct. 31, 2020	Nov. 30, 2019 gal	Sep. 30, 2017 Petition	Apr. 30, 2017 Petition	Aug. 31, 2016 T	Dec. 31, 2023 USD ($) Facility Product Indicator
Loss Contingencies [Line Items]
Measurement of groundwater withdrawals | gal			3,000,000
Number of manufacturing gas plant decommissioned sites that contain residues of byproduct chemicals | Product							4
Estimated environmental remediation activities at manufacturing gas plant sites | $							$ 6
Environmental remediation costs recognized in regulatory assets | $							$ 35
Number of facilities inactive subject to final rule							3
Unfavorable Regulatory Action | CWA
Loss Contingencies [Line Items]
Number of mandatory facility specific factors | Indicator							5
Number of optional facility specific factors | Indicator							6
Electric generating stations with water withdrawals with heightened entrainment analysis under CWA | MGD	2,000,000
Unfavorable Regulatory Action | DESC | CWA
Loss Contingencies [Line Items]
Number of DESC facilities subject to final regulations	5
Carbon Regulations
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T						75,000
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	125,000,000
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
EPA | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category | Minimum [Member]
Loss Contingencies [Line Items]
Loss contingencies individual circumstances period		2021
EPA | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category | Maximum [Member]
Loss Contingencies [Line Items]
Loss contingencies individual circumstances period		2028
Environmental Protection Agency And State Regulatory Agencies | Hydroelectric Facilities
Loss Contingencies [Line Items]
Number of DESC hydroelectric facilities subject to regulations	5