Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2021

Retirement Benefits [Abstract]

Schedule of Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three and nine months ended September 30, 2021 and 2020 are presented in the following tables.

	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Three Months Ended September 30, 2021
Pension Plans
Service cost	$	109	$	26	$	28	$	4	$	2	$	10
Interest cost	87		20		26		4		2		6
Expected return on plan assets	(298)		(72)		(94)		(14)		(4)		(21)
Amortization:
Prior service costs	—		—		—		—		—		(1)
Regulatory asset	—		—		—		—		—		3
Net (gain)/loss	78		21		25		4		1		3
Net periodic pension cost (income)	$	(24)	$	(5)	$	(15)	$	(2)	$	1	$	—
Postretirement Benefits
Service cost	$	6	$	2	$	2	$	1	$	1	$	—
Interest cost	9		2		3		—		—		1
Expected return on plan assets	(19)		(8)		(7)		(1)		—		(2)
Amortization:
Regulatory asset	—		—		—		—		—		2
Net (gain)/loss	1		—		1		—		—		(1)
Net periodic postretirement benefit cost (income)	$	(3)	$	(4)	$	(1)	$	—	$	1	$	—
Nine Months Ended September 30, 2021
Pension Plans
Service cost	$	326	$	77	$	84	$	13	$	7	$	28
Interest cost	260		61		78		12		4		18
Expected return on plan assets	(893)		(215)		(282)		(41)		(11)		(64)
Amortization:
Prior service costs	—		—		1		—		—		(2)
Regulatory asset	—		—		—		—		—		11
Net (gain)/loss	235		62		75		11		3		9
Net periodic pension cost (income)	$	(72)	$	(15)	$	(44)	$	(5)	$	3	$	—
Postretirement Benefits
Service cost	$	18	$	5	$	5	$	1	$	1	$	1
Interest cost	26		6		9		1		—		3
Expected return on plan assets	(57)		(22)		(20)		(2)		—		(6)
Amortization:
Prior service costs	(1)		—		—		—		—		—
Regulatory asset	—		—		—		—		—		5
Net (gain)/loss	3		—		2		—		—		(2)
Net periodic postretirement benefit cost (income)	$	(11)	$	(11)	$	(4)	$	—	$	1	$	1

	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Three Months Ended September 30, 2020
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 (income)	$	2	$	(2)	$	—	$	—	$	1	$	1
Nine Months Ended September 30, 2020
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 (income)	$	4	$	(7)	$	1	$	1	$	1	$	4