Components of the net periodic benefit costs for the three and nine months ended September 30, 2018 and 2017 are presented in the following tables.



Three Months Ended September 30, 2018	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	90		$	19		$	22		$	4		$	5		$	3		$	8
Interest cost	116			26			34			5			5			1			10
Expected return on plan assets	(236		)	(51		)	(74		)	(10		)	(11		)	(3		)	(18		)
Amortization:
Prior service costs	1			—			1			—			—			—			(1		)
Regulatory asset	—			—			—			—			—			—			4
Net (gain)/loss	53			13			18			2			3			—			3
Net periodic pension cost (income)	$	24		$	7		$	1		$	1		$	2		$	1		$	6
Postretirement Benefits
Service cost	$	6		$	1		$	2		$	—		$	—		$	1		$	—
Interest cost	19			5			7			1			—			—			2
Expected return on plan assets	(17		)	(7		)	(6		)	—			—			—			(1		)
Amortization:
Prior service costs	2			1			—			—			—			—			—
Regulatory asset	—			—			—			—			—			—			2
Net (gain)/loss	3			—			2			—			—			—			—
Net periodic postretirement benefit cost	$	13		$	—		$	5		$	1		$	—		$	1		$	3



Nine Months Ended September 30, 2018	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	269		$	58		$	65		$	12		$	13		$	7		$	24
Interest cost	348			76			104			15			15			4			29
Expected return on plan assets	(707		)	(155		)	(222		)	(30		)	(31		)	(8		)	(53		)
Amortization:
Prior service costs	3			1			2			—			—			—			(2		)
Regulatory asset	—			—			—			—			—			—			11
Net (gain)/loss	160			40			52			7			8			1			9
Net periodic pension cost (income)	$	73		$	20		$	1		$	4		$	5		$	4		$	18
Postretirement Benefits
Service cost	$	18		$	4		$	5		$	1		$	1		$	1		$	1
Interest cost	56			13			21			2			2			—			7
Expected return on plan assets	(51		)	(20		)	(19		)	(1		)	(1		)	—			(5		)
Amortization:
Prior service costs	5			3			1			—			—			—			—
Regulatory asset	—			—			—			—			—			—			5
Net (gain)/loss	10			1			6			—			—			—			—
Net periodic postretirement benefit cost	$	38		$	1		$	14		$	2		$	2		$	1		$	8



Three Months Ended September 30, 2017^(*)	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	73		$	15		$	19		$	3		$	4		$	6
Interest cost	114			25			34			5			5			10
Expected return on plan assets	(224		)	(49		)	(71		)	(10		)	(9		)	(18		)
Amortization:
Prior service costs	3			1			—			—			—			—
Net (gain)/loss	41			10			15			2			1			5
Net periodic pension cost (income)	$	7		$	2		$	(3	)	$	—		$	1		$	3
Postretirement Benefits
Service cost	$	6		$	1		$	2		$	—		$	—		$	1
Interest cost	19			4			6			1			1			3
Expected return on plan assets	(16		)	(5		)	(6		)	—			—			(2		)
Amortization:
Prior service costs	2			1			—			—			—			(1		)
Net (gain)/loss	3			—			3			—			—			1
Net periodic postretirement benefit cost	$	14		$	1		$	5		$	1		$	1		$	2


(*)	Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.



Nine Months Ended September 30, 2017^(*)	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	220		$	47		$	56		$	10		$	11		$	17
Interest cost	341			73			103			15			15			30
Expected return on plan assets	(673		)	(147		)	(212		)	(29		)	(29		)	(53		)
Amortization:
Prior service costs	9			2			2			—			1			(1		)
Net (gain)/loss	122			31			43			5			5			15
Net periodic pension cost (income)	$	19		$	6		$	(8	)	$	1		$	3		$	8
Postretirement Benefits
Service cost	$	18		$	4		$	5		$	1		$	1		$	2
Interest cost	59			13			21			2			3			8
Expected return on plan assets	(49		)	(19		)	(18		)	(1		)	(1		)	(5		)
Amortization:
Prior service costs	5			3			1			—			—			(2		)
Net (gain)/loss	10			1			6			—			—			3
Net periodic postretirement benefit cost	$	43		$	2		$	15		$	2		$	3		$	6


(*)	Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.