FINANCING - Maturities of Long-Term Debt (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2019
Debt Instrument [Line Items]
2022	$ 2,157,000,000
2023	3,738,000,000
2024	2,280,000,000
2025	1,199,000,000
2026	3,723,000,000
Series 2019A Remarketable Junior Subordinated Notes \| Junior subordinated notes
Debt Instrument [Line Items]
Debt instrument, face amount		$ 1,725,000,000
Alabama Power
Debt Instrument [Line Items]
2022	751,000,000
2023	301,000,000
2024	22,000,000
2025	250,000,000
2026	45,000,000
Georgia Power
Debt Instrument [Line Items]
2022	676,000,000
2023	897,000,000
2024	498,000,000
2025	145,000,000
2026	441,000,000
Mississippi Power
Debt Instrument [Line Items]
2022	1,000,000
2023	1,000,000
2024	201,000,000
2025	11,000,000
2026	1,000,000
Southern Power
Debt Instrument [Line Items]
2022	677,000,000
2023	290,000,000
2024	0
2025	500,000,000
2026	964,000,000
Southern Power \| Euro-denominated Debt
Debt Instrument [Line Items]
2026	564,000,000
Southern Company Gas
Debt Instrument [Line Items]
2022	46,000,000
2023	400,000,000
2024	0
2025	300,000,000
2026	$ 530,000,000

Face (par) amount of debt instrument at time of issuance.

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