FINANCING - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt, gross	$ 52,100	$ 48,300
Finance lease obligations	215	231
Unamortized fair value adjustment	359	393
Unamortized debt premium (discount), net	(216)	(201)
Unamortized debt issuance expense	(243)	(237)
Total long-term debt	52,277	48,580
Less: Amount due within one year	2,157	3,507
Long-Term Debt	$ 50,120	45,073
Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.62%
Long-term debt, gross	$ 33,120	30,850
Junior subordinated notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.00%
Long-term debt, gross	$ 8,918	7,295
FFB loans
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.88%
Long-term debt, gross	$ 4,962	4,618
Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.05%
Long-term debt, gross	$ 2,662	2,675
First mortgage bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.53%
Long-term debt, gross	$ 2,100	1,900
Medium-term notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	7.60%
Long-term debt, gross	$ 130	160
Other long-term debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.79%
Long-term debt, gross	$ 270	370
Other revenue bonds
Debt Instrument [Line Items]
Long-term debt, gross	0	320
Affiliated trusts
Debt Instrument [Line Items]
Long-term debt, gross	0	206
Alabama Power
Debt Instrument [Line Items]
Long-term debt, gross	9,700	8,900
Finance lease obligations	4	5
Unamortized debt premium (discount), net	(18)	(16)
Unamortized debt issuance expense	(64)	(56)
Total long-term debt	9,687	8,869
Less: Amount due within one year	751	311
Long-Term Debt	$ 8,936	8,558
Alabama Power \| Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.89%
Long-term debt, gross	$ 8,725	7,625
Alabama Power \| Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.55%
Long-term debt, gross	$ 995	1,060
Alabama Power \| Other long-term debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.24%
Long-term debt, gross	$ 45	45
Alabama Power \| Affiliated trusts
Debt Instrument [Line Items]
Long-term debt, gross	0	206
Georgia Power
Debt Instrument [Line Items]
Long-term debt, gross	13,600	12,800
Finance lease obligations	136	145
Unamortized debt premium (discount), net	(11)	(12)
Unamortized debt issuance expense	(114)	(114)
Total long-term debt	13,784	12,970
Less: Amount due within one year	675	542
Long-Term Debt	$ 13,109	12,428
Georgia Power \| Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.61%
Long-term debt, gross	$ 6,825	6,400
Georgia Power \| Junior subordinated notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.00%
Long-term debt, gross	$ 270	270
Georgia Power \| FFB loans
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.88%
Long-term debt, gross	$ 4,962	4,618
Georgia Power \| Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.33%
Long-term debt, gross	$ 1,591	1,538
Georgia Power \| Other long-term debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.70%
Long-term debt, gross	$ 125	125
Mississippi Power
Debt Instrument [Line Items]
Long-term debt, gross	1,500	1,400
Finance lease obligations	18	19
Unamortized debt premium (discount), net	2	11
Unamortized debt issuance expense	(10)	(7)
Total long-term debt	1,511	1,419
Less: Amount due within one year	1	406
Long-Term Debt	$ 1,510	1,013
Mississippi Power \| Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.43%
Long-term debt, gross	$ 1,425	900
Mississippi Power \| Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.86%
Long-term debt, gross	$ 76	76
Mississippi Power \| Other long-term debt
Debt Instrument [Line Items]
Long-term debt, gross	0	100
Mississippi Power \| Other revenue bonds
Debt Instrument [Line Items]
Long-term debt, gross	0	320
Southern Power
Debt Instrument [Line Items]
Long-term debt, gross	3,700	3,700
Finance lease obligations	0	0
Unamortized debt premium (discount), net	(6)	(6)
Unamortized debt issuance expense	(17)	(16)
Total long-term debt	3,688	3,692
Less: Amount due within one year	679	299
Long-Term Debt	3,009	3,393
Fair value gain (loss)	5	109
Derivative notional amount, receive	$ 1,100
Southern Power \| Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.74%
Long-term debt, gross	$ 3,711	3,714
Southern Company Gas
Debt Instrument [Line Items]
Long-term debt, gross	6,900	6,600
Finance lease obligations	0	0
Unamortized fair value adjustment	359	393
Unamortized debt premium (discount), net	(35)	(27)
Total long-term debt	6,902	6,626
Less: Amount due within one year	47	333
Long-Term Debt	$ 6,855	6,293
Southern Company Gas \| Senior notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.96%
Long-term debt, gross	$ 4,348	4,200
Southern Company Gas \| First mortgage bonds
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.53%
Long-term debt, gross	$ 2,100	1,900
Southern Company Gas \| Medium-term notes
Debt Instrument [Line Items]
Weighted Average Interest Rate	7.60%
Long-term debt, gross	$ 130	$ 160

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount (premium).

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