Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2023

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, 2023 and 2022 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, 2023
Pension Plans
Service cost	$	69	$	16	$	17	$	2	$	2	$	6
Interest cost	156		37		48		7		2		11
Expected return on plan assets	(307)		(75)		(97)		(13)		(4)		(22)
Amortization:
Prior service costs	—		—		—		—		—		(1)
Regulatory asset	—		—		—		—		—		4
Net (gain) loss	8		2		4		1		—		(1)
Net periodic pension income	$	(74)	$	(20)	$	(28)	$	(3)	$	—	$	(3)
Postretirement Benefits
Service cost	$	4	$	1	$	1	$	—	$	—	$	—
Interest cost	18		5		6		1		—		2
Expected return on plan assets	(21)		(9)		(7)		(1)		—		(2)
Amortization:
Prior service costs	—		—		1		—		—		—
Regulatory asset	—		—		—		—		—		2
Net gain	(4)		(1)		(1)		—		—		(1)
Net periodic postretirement benefit cost (income)	$	(3)	$	(4)	$	—	$	—	$	—	$	1
Nine Months Ended September 30, 2023
Pension Plans
Service cost	$	207	$	48	$	51	$	8	$	5	$	18
Interest cost	469		109		143		21		6		32
Expected return on plan assets	(922)		(223)		(289)		(41)		(12)		(65)
Amortization:
Prior service costs	—		—		1		—		—		(2)
Regulatory asset	—		—		—		—		—		11
Net (gain) loss	24		7		10		1		—		(3)
Net periodic pension income	$	(222)	$	(59)	$	(84)	$	(11)	$	(1)	$	(9)
Postretirement Benefits
Service cost	$	11	$	3	$	3	$	—	$	—	$	1
Interest cost	53		13		19		2		—		6
Expected return on plan assets	(62)		(26)		(22)		(1)		—		(5)
Amortization:
Prior service costs	1		—		1		—		—		—
Regulatory asset	—		—		—		—		—		5
Net gain	(10)		(2)		(3)		—		—		(3)
Net periodic postretirement benefit cost (income)	$	(7)	$	(12)	$	(2)	$	1	$	—	$	4

	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Three Months Ended September 30, 2022
Pension Plans
Service cost	$	103	$	25	$	26	$	5	$	2	$	9
Interest cost	102		24		31		5		2		7
Expected return on plan assets	(316)		(77)		(99)		(15)		(4)		(22)
Amortization:
Prior service costs	—		—		—		—		—		(1)
Regulatory asset	—		—		—		—		—		3
Net loss	60		16		18		2		1		2
Net periodic pension cost (income)	$	(51)	$	(12)	$	(24)	$	(3)	$	1	$	(2)
Postretirement Benefits
Service cost	$	6	$	2	$	2	$	1	$	1	$	—
Interest cost	10		3		4		—		—		1
Expected return on plan assets	(20)		(9)		(8)		—		—		(2)
Amortization:
Prior service costs	(1)		—		—		—		—		—
Regulatory asset	—		—		—		—		—		2
Net (gain)/loss	1		—		—		—		—		(1)
Net periodic postretirement benefit cost (income)	$	(4)	$	(4)	$	(2)	$	1	$	1	$	—
Nine Months Ended September 30, 2022
Pension Plans
Service cost	$	309	$	74	$	78	$	13	$	7	$	26
Interest cost	306		72		92		14		5		21
Expected return on plan assets	(949)		(229)		(298)		(44)		(12)		(68)
Amortization:
Prior service costs	—		—		1		—		—		(2)
Regulatory asset	—		—		—		—		—		11
Net loss	180		47		55		9		2		5
Net periodic pension cost (income)	$	(154)	$	(36)	$	(72)	$	(8)	$	2	$	(7)
Postretirement Benefits
Service cost	$	17	$	5	$	5	$	1	$	1	$	1
Interest cost	31		8		11		1		—		4
Expected return on plan assets	(60)		(25)		(21)		(1)		—		(6)
Amortization:
Prior service costs	(1)		—		—		—		—		—
Regulatory asset	—		—		—		—		—		5
Net (gain) loss	1		—		1		—		—		(2)
Net periodic postretirement benefit cost (income)	$	(12)	$	(12)	$	(4)	$	1	$	1	$	2