Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Expires, 2019	$ 163,000,000
Expires, 2020	500,000,000
Expires, 2022	7,200,000,000
Total	7,863,000,000
Unused	7,834,000,000
Southern Company
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
ALABAMA POWER CO
Line of Credit Facility [Line Items]
Expires, 2019	33,000,000
Expires, 2020	500,000,000
Expires, 2022	800,000,000
Total	1,333,000,000
Unused	1,333,000,000
GEORGIA POWER CO
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,750,000,000
Total	1,750,000,000
Unused	1,736,000,000
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
Expires, 2019	100,000,000
Expires, 2020	0
Expires, 2022	0
Total	100,000,000
Unused	100,000,000
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	750,000,000
Total	750,000,000
Unused	741,000,000
SOUTHERN POWER CO | Standby Letters of Credit
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	24,000,000
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,900,000,000
Total	1,900,000,000
Unused	1,895,000,000
Other
Line of Credit Facility [Line Items]
Expires, 2019	30,000,000
Expires, 2020	0
Expires, 2022	0
Total	30,000,000
Unused	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,400,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 500,000,000