FINANCING - Bank Credit Arrangements (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Expires, 2020	$ 33,000,000
Expires, 2022	675,000,000
Expires, 2024	6,900,000,000
Total	7,608,000,000
Unused	7,576,000,000
Due within One Year	33,000,000
Southern Company
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	0
Expires, 2024	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Due within One Year	0
Alabama Power
Line of Credit Facility [Line Items]
Expires, 2020	3,000,000
Expires, 2022	525,000,000
Expires, 2024	800,000,000
Total	1,328,000,000
Unused	1,328,000,000
Due within One Year	3,000,000
Georgia Power
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	0
Expires, 2024	1,750,000,000
Total	1,750,000,000
Unused	1,733,000,000
Due within One Year	0
Mississippi Power
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	150,000,000
Expires, 2024	0
Total	150,000,000
Unused	150,000,000
Due within One Year	0
Southern Power
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	0
Expires, 2024	600,000,000
Total	600,000,000
Unused	591,000,000
Due within One Year	0
Southern Power | Continuing Letter of Credit Facility
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	97,000,000	$ 103,000,000
Southern Company Gas
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	0
Expires, 2024	1,750,000,000
Total	1,750,000,000
Unused	1,745,000,000
Due within One Year	0
Other Subsidiaries
Line of Credit Facility [Line Items]
Expires, 2020	30,000,000
Expires, 2022	0
Expires, 2024	0
Total	30,000,000
Unused	30,000,000
Due within One Year	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,250,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 500,000,000