Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2019

Retirement Benefits [Abstract]

Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three and nine months ended September 30, 2019 and 2018 are presented in the following tables.

Three Months Ended September 30, 2019	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	73		$	17		$	19		$	3		$	2		$	7
Interest cost	123			28			38			6			1			9
Expected return on plan assets	(222		)	(51		)	(73		)	(10		)	(2		)	(15		)
Amortization:
Prior service costs	1			—			—			—			—			(1		)
Regulatory asset	—			—			—			—			—			3
Net (gain)/loss	30			9			11			1			—			1
Net periodic pension cost (income)	$	5		$	3		$	(5	)	$	—		$	1		$	4
Postretirement Benefits
Service cost	$	5		$	1		$	2		$	1		$	—		$	—
Interest cost	18			4			6			—			—			2
Expected return on plan assets	(16		)	(6		)	(7		)	—			—			(1		)
Amortization:
Prior service costs	—			1			—			—			—			—
Regulatory asset	—			—			—			—			—			1
Net (gain)/loss	(1		)	—			1			—			—			—
Net periodic postretirement benefit cost	$	6		$	—		$	2		$	1		$	—		$	2

Nine Months Ended September 30, 2019	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power			Southern Company Gas
	(in millions)
Pension Plans
Service cost	$	219		$	51		$	56		$	9		$	5		$	19
Interest cost	369			85			116			17			4			27
Expected return on plan assets	(664		)	(154		)	(219		)	(30		)	(7		)	(45		)
Amortization:
Prior service costs	2			1			1			—			—			(2		)
Regulatory asset	—			—			—			—			—			10
Net (gain)/loss	90			27			33			4			—			2
Net periodic pension cost (income)	$	16		$	10		$	(13	)	$	—		$	2		$	11
Postretirement Benefits
Service cost	$	14		$	3		$	4		$	1		$	—		$	1
Interest cost	52			12			19			2			—			7
Expected return on plan assets	(49		)	(19		)	(19		)	(1		)	—			(4		)
Amortization:
Prior service costs	2			3			—			—			—			—
Regulatory asset	—			—			—			—			—			4
Net (gain)/loss	(2		)	—			1			—			—			(2		)
Net periodic postretirement benefit cost	$	17		$	(1	)	$	5		$	2		$	—		$	6

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

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