LEASES - Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases (Details) $ in Millions	Dec. 31, 2020 USD ($)
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	$ 207
2022	187
2023	138
2024	106
2025	99
Thereafter	978
Total	1,715
Alabama Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	83
2022	76
2023	32
2024	4
2025	3
Thereafter	23
Total	221
Georgia Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	19
2022	8
2023	2
2024	0
2025	0
Thereafter	0
Total	29
Southern Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	86
2022	87
2023	88
2024	90
2025	74
Thereafter	313
Total	738
Southern Company Gas
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	35
2022	35
2023	34
2024	33
2025	28
Thereafter	435
Total	$ 600

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- Definition

Amount of lease payments to be received by lessor for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919396-209981

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- Definition

Amount of lease payment to be received by lessor for operating lease in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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Amount of lease payment to be received by lessor for operating lease in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of lease payment to be received by lessor for operating lease in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of lease payment to be received by lessor for operating lease in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of lease payment to be received by lessor for operating lease in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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