RETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Amortization:
Net (gain)/loss
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0		$ 0
Pension Plans and Postretirement Plans
Service cost	94,000,000	73,000,000	188,000,000	$ 146,000,000
Interest cost	108,000,000	123,000,000	216,000,000	246,000,000
Expected return on plan assets	(275,000,000)	(221,000,000)	(550,000,000)	(442,000,000)
Amortization:
Prior service costs	0	1,000,000	1,000,000	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	67,000,000	30,000,000	134,000,000	60,000,000
Net periodic pension cost (income)	(6,000,000)	6,000,000	(11,000,000)	11,000,000
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	22,000,000	17,000,000	44,000,000	34,000,000
Interest cost	25,000,000	29,000,000	50,000,000	57,000,000
Expected return on plan assets	(66,000,000)	(52,000,000)	(132,000,000)	(103,000,000)
Amortization:
Prior service costs	0	1,000,000	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	18,000,000	9,000,000	36,000,000	18,000,000
Net periodic pension cost (income)	(1,000,000)	4,000,000	(2,000,000)	7,000,000
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	24,000,000	18,000,000	48,000,000	37,000,000
Interest cost	34,000,000	39,000,000	67,000,000	78,000,000
Expected return on plan assets	(87,000,000)	(73,000,000)	(174,000,000)	(146,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	1,000,000	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	21,000,000	11,000,000	43,000,000	22,000,000
Net periodic pension cost (income)	(7,000,000)	(4,000,000)	(15,000,000)	(8,000,000)
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000	8,000,000	6,000,000
Interest cost	5,000,000	5,000,000	10,000,000	11,000,000
Expected return on plan assets	(12,000,000)	(10,000,000)	(25,000,000)	(20,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	3,000,000	2,000,000	6,000,000	3,000,000
Net periodic pension cost (income)	0	0	(1,000,000)	0
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	1,000,000	4,000,000	3,000,000
Interest cost	2,000,000	2,000,000	3,000,000	3,000,000
Expected return on plan assets	(3,000,000)	(3,000,000)	(6,000,000)	(5,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	1,000,000	0
Net periodic pension cost (income)	1,000,000	0	2,000,000	1,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	8,000,000	6,000,000	16,000,000	12,000,000
Interest cost	7,000,000	9,000,000	15,000,000	18,000,000
Expected return on plan assets	(20,000,000)	(15,000,000)	(39,000,000)	(30,000,000)
Amortization:
Prior service costs	0	0	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000	4,000,000	8,000,000	7,000,000
Net (gain)/loss	3,000,000	0	5,000,000	1,000,000
Net periodic pension cost (income)	2,000,000	4,000,000	4,000,000	7,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	6,000,000	4,000,000	11,000,000	9,000,000
Interest cost	14,000,000	17,000,000	27,000,000	34,000,000
Expected return on plan assets	(18,000,000)	(17,000,000)	(36,000,000)	(33,000,000)
Amortization:
Prior service costs	(1,000,000)	1,000,000	(1,000,000)	2,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	1,000,000	(1,000,000)
Net periodic pension cost (income)	1,000,000	5,000,000	2,000,000	11,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	3,000,000	2,000,000
Interest cost	3,000,000	4,000,000	6,000,000	8,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)	(14,000,000)	(13,000,000)
Amortization:
Prior service costs	0	1,000,000	0	2,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	(3,000,000)	(1,000,000)	(5,000,000)	(1,000,000)
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	1,000,000	3,000,000	2,000,000
Interest cost	5,000,000	6,000,000	10,000,000	13,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)	(13,000,000)	(12,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	1,000,000	0
Net periodic pension cost (income)	1,000,000	1,000,000	1,000,000	3,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	0	1,000,000	0
Interest cost	1,000,000	1,000,000	1,000,000	2,000,000
Expected return on plan assets	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	1,000,000	0	1,000,000	1,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0	0	0
Interest cost	0	0	0	0
Expected return on plan assets	0	0	0	0
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	0	0	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	1,000,000	0	1,000,000	1,000,000
Interest cost	4,000,000	3,000,000	6,000,000	5,000,000
Expected return on plan assets	(2,000,000)	(1,000,000)	(4,000,000)	(3,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	1,000,000	1,000,000	3,000,000	3,000,000
Net (gain)/loss	(1,000,000)	(1,000,000)	(2,000,000)	(2,000,000)
Net periodic pension cost (income)	$ 3,000,000	$ 2,000,000	$ 4,000,000	$ 4,000,000