Regulatory Matters (Narrative) (Detail) ft³ in Millions, customer in Millions, $ in Millions		1 Months Ended								12 Months Ended
	May 03, 2019 USD ($)	Nov. 01, 2019 USD ($)	Apr. 30, 2019 ft³	Mar. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Nov. 30, 2013 kV mi	Dec. 31, 2011	Dec. 31, 2007 customer	Dec. 31, 2018 USD ($)
SCE&G [Member]
Public Utilities General Disclosures [Line Items]
Recover of cost and net lost revenue with incentive						$ 30
Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Submitted and approved decrease in base rate revenue							$ 14
Regulatory liabilities one time bill credit amount							$ 13
Virginia Electric and Power Company | Virginia Regulation
Public Utilities General Disclosures [Line Items]
Proposed annual revenue reduction amount						$ 171
Interim rate reduction amount								$ 125
Annual revenue reduction amount				$ 183
Estimated annual revenue reduction on one-time customer credit				$ 135
Return of equity percentage				10.75%
Virginia Electric and Power Company | Virginia Regulation | Surry Switching Station Transmission Line
Public Utilities General Disclosures [Line Items]
Length of transmission line (miles) | mi									7
Capacity of transmission line (kV) | kV									500
Virginia Electric and Power Company | Virginia Regulation | Transmission Line from Skiffes Creek Switching Station to Wheaton Substation
Public Utilities General Disclosures [Line Items]
Length of transmission line (miles) | mi									20
Capacity of transmission line (kV) | kV									230
Virginia Electric and Power Company | Virginia Regulation | Rider U
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement				$ 52
Virginia Electric and Power Company | Virginia Regulation | Rider U | Fourth Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment				$ 123
Virginia Electric and Power Company | Virginia Regulation | Solar Development Project | Rider US-3 | Operating Segments
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement								$ 10
Virginia Electric and Power Company | North Carolina Regulation
Public Utilities General Disclosures [Line Items]
Return of equity percentage				10.75%
Percentage of earned return				7.52%
Authorized return percentage				9.90%
Virginia Electric and Power Company | North Carolina Regulation | Scenario Forecast | Annual Base Fuel Revenues
Public Utilities General Disclosures [Line Items]
Increase (decrease) in revenue requirement		$ 27
East Ohio | Ohio Regulation | Pipeline Infrastructure Replacement Program
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement					$ 190
Percentage replacement of pipeline system					25.00%
Total estimated cost					$ 1,600							$ 202
East Ohio | Ohio Regulation | Automated Meter Reading Program
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement				$ 4
Number of customers with automated meter reading technology | customer											1.2
East Ohio | Ohio Regulation | CEP Program
Public Utilities General Disclosures [Line Items]
Percentage to defer expenses on capital investments										6.50%
East Ohio | Ohio Regulation | CEP Program | Subsequent Event
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement	$ 83
Total estimated cost	$ 723
Questar Gas | Utah And Wyoming Regulation | Subsequent Event
Public Utilities General Disclosures [Line Items]
LNG storage facility, liquefaction rate per day | ft³			8.2
Number of days to make prudency determination			180 days
Cove Point | Federal Energy Regulatory Commission
Public Utilities General Disclosures [Line Items]
Annual transportation cost rate adjustment, approval amount requested to recover amount					$ 24