RETIREMENT BENEFITS (Tables)

9 Months Ended

Sep. 30, 2020

Retirement Benefits [Abstract]

Pension Plans and Postretirement Plans

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

Three Months Ended September 30, 2020	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	94	$	23	$	24	$	3	$	2	$	8
Interest cost	108		25		33		5		1		8
Expected return on plan assets	(274)		(66)		(87)		(13)		(4)		(20)
Amortization:
Prior service costs	—		1		—		—		—		(1)
Regulatory asset	—		—		—		—		—		4
Net (gain)/loss	67		17		22		4		1		2
Net periodic pension cost (income)	$	(5)	$	—	$	(8)	$	(1)	$	—	$	1
Postretirement Benefits
Service cost	$	6	$	1	$	2	$	(1)	$	1	$	—
Interest cost	13		4		5		1		—		2
Expected return on plan assets	(18)		(7)		(7)		—		—		(2)
Amortization:
Prior service costs	—		—		(1)		—		—		—
Regulatory asset	—		—		—		—		—		2
Net (gain)/loss	1		—		1		—		—		(1)
Net periodic postretirement benefit cost	$	2	$	(2)	$	—	$	—	$	1	$	1

Nine Months Ended September 30, 2020	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	282	$	67	$	72	$	11	$	6	$	24
Interest cost	324		75		100		15		4		23
Expected return on plan assets	(824)		(198)		(261)		(38)		(10)		(59)
Amortization:
Prior service costs	1		1		1		—		—		(2)
Regulatory asset	—		—		—		—		—		12
Net (gain)/loss	201		53		65		10		2		7
Net periodic pension cost (income)	$	(16)	$	(2)	$	(23)	$	(2)	$	2	$	5
Postretirement Benefits
Service cost	$	17	$	4	$	5	$	—	$	1	$	1
Interest cost	40		10		15		2		—		5
Expected return on plan assets	(54)		(21)		(20)		(1)		—		(5)
Amortization:
Prior service costs	(1)		—		(1)		—		—		—
Regulatory asset	—		—		—		—		—		5
Net (gain)/loss	2		—		2		—		—		(2)
Net periodic postretirement benefit cost	$	4	$	(7)	$	1	$	1	$	1	$	4

Three Months Ended September 30, 2019	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	73	$	17	$	19	$	3	$	2	$	7
Interest cost	123		28		38		6		1		9
Expected return on plan assets	(222)		(51)		(73)		(10)		(2)		(15)
Amortization:
Prior service costs	1		—		—		—		—		(1)
Regulatory asset	—		—		—		—		—		3
Net (gain)/loss	30		9		11		1		—		1
Net periodic pension cost (income)	$	5	$	3	$	(5)	$	—	$	1	$	4
Postretirement Benefits
Service cost	$	5	$	1	$	2	$	1	$	—	$	—
Interest cost	18		4		6		—		—		2
Expected return on plan assets	(16)		(6)		(7)		—		—		(1)
Amortization:
Prior service costs	—		1		—		—		—		—
Regulatory asset	—		—		—		—		—		1
Net (gain)/loss	(1)		—		1		—		—		—
Net periodic postretirement benefit cost	$	6	$	—	$	2	$	1	$	—	$	2

Nine Months Ended September 30, 2019	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	219	$	51	$	56	$	9	$	5	$	19
Interest cost	369		85		116		17		4		27
Expected return on plan assets	(664)		(154)		(219)		(30)		(7)		(45)
Amortization:
Prior service costs	2		1		1		—		—		(2)
Regulatory asset	—		—		—		—		—		10
Net (gain)/loss	90		27		33		4		—		2
Net periodic pension cost (income)	$	16	$	10	$	(13)	$	—	$	2	$	11
Postretirement Benefits
Service cost	$	14	$	3	$	4	$	1	$	—	$	1
Interest cost	52		12		19		2		—		7
Expected return on plan assets	(49)		(19)		(19)		(1)		—		(4)
Amortization:
Prior service costs	2		3		—		—		—		—
Regulatory asset	—		—		—		—		—		4
Net (gain)/loss	(2)		—		1		—		—		(2)
Net periodic postretirement benefit cost	$	17	$	(1)	$	5	$	2	$	—	$	6