Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Pension Plans and Postretirement Plans

Components of the net periodic benefit costs for the three months ended March 31, 2016 were as follows:

Pension Plans	Southern Company			Alabama Power			Georgia Power			Gulf Power			Mississippi Power
	(in millions)
Three Months Ended March 31, 2016
Service cost	$	62		$	14		$	17		$	3		$	3
Interest cost	100			24			34			5			5
Expected return on plan assets	(187		)	(46		)	(64		)	(9		)	(9		)
Amortization:
Prior service costs	4			1			1			—			—
Net (gain)/loss	38			10			14			2			2
Net cost	$	17		$	3		$	2		$	1		$	1
Three Months Ended March 31, 2015
Service cost	$	64		$	15		$	18		$	3		$	3
Interest cost	111			26			38			5			5
Expected return on plan assets	(181		)	(45		)	(63		)	(8		)	(8		)
Amortization:
Prior service costs	6			2			3			—			—
Net (gain)/loss	54			14			19			3			3
Net cost	$	54		$	12		$	15		$	3		$	3

Postretirement Benefits	Southern Company			Alabama Power			Georgia Power			Gulf Power		Mississippi Power
	(in millions)
Three Months Ended March 31, 2016
Service cost	$	5		$	1		$	2		$	—	$	—
Interest cost	18			5			8			1		1
Expected return on plan assets	(14		)	(6		)	(6		)	—		—
Amortization:
Prior service costs	2			1			—			—		—
Net (gain)/loss	3			—			2			—		—
Net cost	$	14		$	1		$	6		$	1	$	1
Three Months Ended March 31, 2015
Service cost	$	6		$	1		$	2		$	—	$	—
Interest cost	19			5			8			1		1
Expected return on plan assets	(15		)	(6		)	(6		)	—		—
Amortization:
Prior service costs	1			1			—			—		—
Net (gain)/loss	5			—			3			—		—
Net cost	$	16		$	1		$	7		$	1	$	1