RETIREMENT BENEFITS (Tables)

6 Months Ended

Jun. 30, 2020

Retirement Benefits [Abstract]

Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three and six months ended June 30, 2020 and 2019 are presented in the following tables.

Three Months Ended June 30, 2020	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	94		$	22		$	24		$	4		$	2		$	8
Interest cost	108			25			34			5			2			7
Expected return on plan assets	(275		)	(66		)	(87		)	(12		)	(3		)	(20		)
Amortization:
Prior service costs	—			—			1			—			—			—
Regulatory asset	—			—			—			—			—			4
Net (gain)/loss	67			18			21			3			—			3
Net periodic pension cost (income)	$	(6	)	$	(1	)	$	(7	)	$	—		$	1		$	2
Postretirement Benefits
Service cost	$	6		$	1		$	2		$	1		$	—		$	1
Interest cost	14			3			5			1			—			4
Expected return on plan assets	(18		)	(7		)	(6		)	(1		)	—			(2		)
Amortization:
Prior service costs	(1		)	—			—			—			—			—
Regulatory asset	—			—			—			—			—			1
Net (gain)/loss	—			—			—			—			—			(1		)
Net periodic postretirement benefit cost	$	1		$	(3	)	$	1		$	1		$	—		$	3

Six Months Ended June 30, 2020	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	188		$	44		$	48		$	8		$	4		$	16
Interest cost	216			50			67			10			3			15
Expected return on plan assets	(550		)	(132		)	(174		)	(25		)	(6		)	(39		)
Amortization:
Prior service costs	1			—			1			—			—			(1		)
Regulatory asset	—			—			—			—			—			8
Net (gain)/loss	134			36			43			6			1			5
Net periodic pension cost (income)	$	(11	)	$	(2	)	$	(15	)	$	(1	)	$	2		$	4

Six Months Ended June 30, 2020	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power		Southern Company Gas
	(in millions)
Postretirement Benefits
Service cost	$	11		$	3		$	3		$	1		$	—	$	1
Interest cost	27			6			10			1			—		6
Expected return on plan assets	(36		)	(14		)	(13		)	(1		)	—		(4		)
Amortization:
Prior service costs	(1		)	—			—			—			—		—
Regulatory asset	—			—			—			—			—		3
Net (gain)/loss	1			—			1			—			—		(2		)
Net periodic postretirement benefit cost	$	2		$	(5	)	$	1		$	1		$	—	$	4

Three Months Ended June 30, 2019	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	73		$	17		$	18		$	3		$	1		$	6
Interest cost	123			29			39			5			2			9
Expected return on plan assets	(221		)	(52		)	(73		)	(10		)	(3		)	(15		)
Amortization:
Prior service costs	1			1			1			—			—			—
Regulatory asset	—			—			—			—			—			4
Net (gain)/loss	30			9			11			2			—			—
Net periodic pension cost (income)	$	6		$	4		$	(4	)	$	—		$	—		$	4
Postretirement Benefits
Service cost	$	4		$	1		$	1		$	—		$	—		$	—
Interest cost	17			4			6			1			—			3
Expected return on plan assets	(17		)	(7		)	(6		)	(1		)	—			(1		)
Amortization:
Prior service costs	1			1			—			—			—			—
Regulatory asset	—			—			—			—			—			1
Net (gain)/loss	—			—			—			—			—			(1		)
Net periodic postretirement benefit cost	$	5		$	(1	)	$	1		$	—		$	—		$	2

Six Months Ended June 30, 2019	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	146		$	34		$	37		$	6		$	3		$	12
Interest cost	246			57			78			11			3			18
Expected return on plan assets	(442		)	(103		)	(146		)	(20		)	(5		)	(30		)
Amortization:
Prior service costs	1			1			1			—			—			(1		)
Regulatory asset	—			—			—			—			—			7
Net (gain)/loss	60			18			22			3			—			1
Net periodic pension cost (income)	$	11		$	7		$	(8	)	$	—		$	1		$	7
Postretirement Benefits
Service cost	$	9		$	2		$	2		$	—		$	—		$	1
Interest cost	34			8			13			2			—			5
Expected return on plan assets	(33		)	(13		)	(12		)	(1		)	—			(3		)
Amortization:
Prior service costs	2			2			—			—			—			—
Regulatory asset	—			—			—			—			—			3
Net (gain)/loss	(1		)	—			—			—			—			(2		)
Net periodic postretirement benefit cost	$	11		$	(1	)	$	3		$	1		$	—		$	4