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Contract With Customer, Liability, Bill Credits

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Infrastructure Replacement Program, Petitioned Investment Variance Amount

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved return on equity.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Regulatory Matters - Southern Company Gas (Details) $ in Millions					1 Months Ended		12 Months Ended
	Jun. 03, 2019 USD ($)	Apr. 16, 2019 USD ($) intervenor	Apr. 08, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($)	Dec. 31, 2017
Nicor Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount						$ 230
Public utilities, approved return on equity percentage		9.86%				10.60%
Regulatory equity ratio		54.00%				54.00%	52.00%
Number of intervenors \| intervenor		2
Requested increase in rate amounts		$ 180
Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage	10.75%
Regulatory equity ratio	55.00%
Requested increase in rate amounts	$ 96
Virginia Natural Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount					$ (14)
Bill credits				$ 14
Virginia Natural Gas \| SAVE
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			$ 370
Infrastructure replacement program, petitioned investment renewal term			5 years
Infrastructure replacement program, petitioned investment term			6 years
Infrastructure replacement program, proposed investment variance amount			$ 10
Virginia Natural Gas \| SAVE \| 2018
Loss Contingencies [Line Items]
Approved investment amount			35
Virginia Natural Gas \| SAVE \| 2019
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			40
Infrastructure replacement program, proposed investment variance amount			6
Virginia Natural Gas \| SAVE \| 2020
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			50
Infrastructure replacement program, proposed investment variance amount			8
Virginia Natural Gas \| SAVE \| 2021
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			60
Infrastructure replacement program, proposed investment variance amount			9
Virginia Natural Gas \| SAVE \| 2022
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			70
Infrastructure replacement program, proposed investment variance amount			10
Virginia Natural Gas \| SAVE \| 2023
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			70
Infrastructure replacement program, proposed investment variance amount			10
Virginia Natural Gas \| SAVE \| 2024
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount			70
Infrastructure replacement program, proposed investment variance amount			$ 10
Minimum \| Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage	10.55%
Maximum \| Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage	10.95%