Retirement Benefits (Tables)

6 Months Ended

Jun. 30, 2017

Retirement Benefits [Abstract]

Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three and six months ended June 30, 2017 and 2016 are presented in the following tables.

Pension Plans	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power
	(in millions)
Three Months Ended June 30, 2017
Service cost	$	74		$	16		$	18		$	4		$	3
Interest cost	113			24			35			5			5
Expected return on plan assets	(225		)	(49		)	(70		)	(9		)	(10		)
Amortization:
Prior service costs	3			—			1			—			1
Net (gain)/loss	41			11			14			1			2
Net periodic pension cost (income)	$	6		$	2		$	(2	)	$	1		$	1
Six Months Ended June 30, 2017
Service cost	$	147		$	32		$	37		$	7		$	7
Interest cost	227			48			69			10			10
Expected return on plan assets	(449		)	(98		)	(141		)	(19		)	(20		)
Amortization:
Prior service costs	6			1			2			—			1
Net (gain)/loss	81			21			28			3			4
Net periodic pension cost (income)	$	12		$	4		$	(5	)	$	1		$	2
Three Months Ended June 30, 2016
Service cost	$	62		$	15		$	18		$	3		$	3
Interest cost	101			24			34			4			5
Expected return on plan assets	(187		)	(46		)	(65		)	(8		)	(8		)
Amortization:
Prior service costs	3			—			2			1			—
Net (gain)/loss	37			10			13			1			1
Net periodic pension cost	$	16		$	3		$	2		$	1		$	1
Six Months Ended June 30, 2016
Service cost	$	124		$	29		$	35		$	6		$	6
Interest cost	201			48			68			9			10
Expected return on plan assets	(374		)	(92		)	(129		)	(17		)	(17		)
Amortization:
Prior service costs	7			1			3			1			—
Net (gain)/loss	75			20			27			3			3
Net periodic pension cost	$	33		$	6		$	4		$	2		$	2

Pension Plans	Southern Company Gas
	(in millions)
Successor – Three Months Ended June 30, 2017
Service cost	$	5
Interest cost	10
Expected return on plan assets	(17		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	5
Net periodic pension cost	$	2
Successor – Six Months Ended June 30, 2017
Service cost	$	11
Interest cost	20
Expected return on plan assets	(35		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	10
Net periodic pension cost	$	5
Predecessor – Three Months Ended June 30, 2016
Service cost	$	7
Interest cost	11
Expected return on plan assets	(17		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	7
Net periodic pension cost	$	7
Predecessor – Six Months Ended June 30, 2016
Service cost	$	13
Interest cost	21
Expected return on plan assets	(33		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	13
Net periodic pension cost	$	13

Postretirement Benefits	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power
	(in millions)
Three Months Ended June 30, 2017
Service cost	$	6		$	2		$	1		$	1		$	1
Interest cost	20			4			8			—			1
Expected return on plan assets	(17		)	(8		)	(6		)	(1		)	(1		)
Amortization:
Prior service costs	1			1			1			—			—
Net (gain)/loss	5			1			1			—			—
Net periodic postretirement benefit cost	$	15		$	—		$	5		$	—		$	1
Six Months Ended June 30, 2017
Service cost	$	12		$	3		$	3		$	1		$	1
Interest cost	40			9			15			1			2
Expected return on plan assets	(33		)	(14		)	(12		)	(1		)	(1		)
Amortization:
Prior service costs	3			2			1			—			—
Net (gain)/loss	7			1			3			—			—
Net periodic postretirement benefit cost	$	29		$	1		$	10		$	1		$	2
Three Months Ended June 30, 2016
Service cost	$	6		$	2		$	1		$	1		$	1
Interest cost	17			4			7			—			1
Expected return on plan assets	(14		)	(7		)	(5		)	(1		)	(1		)
Amortization:
Prior service costs	1			1			1			—			—
Net (gain)/loss	4			1			2			—			—
Net periodic postretirement benefit cost	$	14		$	1		$	6		$	—		$	1
Six Months Ended June 30, 2016
Service cost	$	11		$	3		$	3		$	1		$	1
Interest cost	35			9			15			1			2
Expected return on plan assets	(28		)	(13		)	(11		)	(1		)	(1		)
Amortization:
Prior service costs	3			2			1			—			—
Net (gain)/loss	7			1			4			—			—
Net periodic postretirement benefit cost	$	28		$	2		$	12		$	1		$	2

Postretirement Benefits	Southern Company Gas
	(in millions)
Successor – Three Months Ended June 30, 2017
Service cost	$	—
Interest cost	2
Expected return on plan assets	(1		)
Amortization:
Prior service costs	—
Net (gain)/loss	1
Net periodic postretirement benefit cost	$	2
Successor – Six Months Ended June 30, 2017
Service cost	$	1
Interest cost	5
Expected return on plan assets	(3		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	2
Net periodic postretirement benefit cost	$	4
Predecessor – Three Months Ended June 30, 2016
Service cost	$	—
Interest cost	2
Expected return on plan assets	(1		)
Amortization:
Prior service costs	—
Net (gain)/loss	1
Net periodic postretirement benefit cost	$	2
Predecessor – Six Months Ended June 30, 2016
Service cost	$	1
Interest cost	5
Expected return on plan assets	(3		)
Amortization:
Prior service costs	(1		)
Net (gain)/loss	2
Net periodic postretirement benefit cost	$	4