Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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The proportionate share of interest (percent) in a jointly owned utility plant.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Regulatory Matters - APC (Details) - USD ($) $ in Millions	Apr. 15, 2021	Mar. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Construction work in progress		$ 9,525	$ 8,697
ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress		1,052	866
ALABAMA POWER CO \| Plant Barry Unit 8
Public Utilities, General Disclosures [Line Items]
Construction work in progress		161
MISSISSIPPI POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress		$ 163	$ 146
MISSISSIPPI POWER CO \| Plant Greene County Units 1 and 2 \| ALABAMA POWER CO \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Proportionate ownership share	40.00%