Retirement Benefits (Tables)

6 Months Ended

Jun. 30, 2021

Retirement Benefits [Abstract]

Schedule of Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three and six months ended June 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 June 30, 2021
Pension Plans
Service cost	$	108	$	25	$	28	$	5	$	3	$	9
Interest cost	86		21		26		4		1		6
Expected return on plan assets	(297)		(71)		(94)		(13)		(4)		(22)
Amortization:
Prior service costs	—		—		1		—		—		—
Regulatory asset	—		—		—		—		—		4
Net (gain)/loss	79		20		25		3		1		3
Net periodic pension cost (income)	$	(24)	$	(5)	$	(14)	$	(1)	$	1	$	—
Postretirement Benefits
Service cost	$	6	$	2	$	1	$	—	$	—	$	1
Interest cost	9		2		3		1		—		1
Expected return on plan assets	(19)		(7)		(6)		(1)		—		(2)
Amortization:
Prior service costs	(1)		—		—		—		—		—
Regulatory asset	—		—		—		—		—		1
Net (gain)/loss	1		—		—		—		—		—
Net periodic postretirement benefit cost (income)	$	(4)	$	(3)	$	(2)	$	—	$	—	$	1
Six Months Ended June 30, 2021
Pension Plans
Service cost	$	217	$	51	$	56	$	9	$	5	$	18
Interest cost	173		41		52		8		2		12
Expected return on plan assets	(595)		(143)		(188)		(27)		(7)		(43)
Amortization:
Prior service costs	—		—		1		—		—		(1)
Regulatory asset	—		—		—		—		—		8
Net (gain)/loss	157		41		50		7		2		6
Net periodic pension cost (income)	$	(48)	$	(10)	$	(29)	$	(3)	$	2	$	—
Postretirement Benefits
Service cost	$	12	$	3	$	3	$	—	$	—	$	1
Interest cost	17		4		6		1		—		2
Expected return on plan assets	(38)		(14)		(13)		(1)		—		(4)
Amortization:
Prior service costs	(1)		—		—		—		—		—
Regulatory asset	—		—		—		—		—		3
Net (gain)/loss	2		—		1		—		—		(1)
Net periodic postretirement benefit cost (income)	$	(8)	$	(7)	$	(3)	$	—	$	—	$	1

	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Three Months Ended June 30, 2020
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 (income)	$	1	$	(3)	$	1	$	1	$	—	$	3
Six Months Ended June 30, 2020
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
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 (income)	$	2	$	(5)	$	1	$	1	$	—	$	4