Components of the net periodic benefit costs for the three months ended March 31, 2018 and 2017 are presented in the following tables.



Three Months Ended March 31, 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		$	4		$	2		$	8
Interest cost	116			25			35			5			5			1			10
Expected return on plan assets	(236		)	(51		)	(74		)	(10		)	(10		)	(3		)	(18		)
Amortization:
Prior service costs	1			—			—			—			—			—			(1		)
Regulatory asset	—			—			—			—			—			—			3
Net (gain)/loss	53			14			17			2			3			1			3
Net periodic pension cost (income)	$	24		$	7		$	—		$	1		$	2		$	1		$	5
Postretirement Benefits
Service cost	$	6		$	1		$	2		$	—		$	—		$	—		$	1
Interest cost	19			4			7			1			1			—			2
Expected return on plan assets	(17		)	(6		)	(6		)	—			—			—			(2		)
Amortization:
Prior service costs	2			1			—			—			—			—			—
Regulatory asset	—			—			—			—			—			—			1
Net (gain)/loss	3			—			2			—			—			—			—
Net periodic postretirement benefit cost	$	13		$	—		$	5		$	1		$	1		$	—		$	2



Three Months Ended March 31, 2017^(*)	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	73		$	16		$	19		$	3		$	4		$	6
Interest cost	114			24			34			5			5			10
Expected return on plan assets	(224		)	(49		)	(71		)	(10		)	(10		)	(18		)
Amortization:
Prior service costs	3			1			1			—			—			—
Net (gain)/loss	40			10			14			2			2			5
Net periodic pension cost (income)	$	6		$	2		$	(3	)	$	—		$	1		$	3
Postretirement Benefits
Service cost	$	6		$	1		$	2		$	—		$	—		$	1
Interest cost	20			5			7			1			1			3
Expected return on plan assets	(16		)	(6		)	(6		)	—			—			(2		)
Amortization:
Prior service costs	2			1			—			—			—			(1		)
Net (gain)/loss	2			—			2			—			—			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.