Common Stock and Stock Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Share-based Compensation, Stock Options, Activity

Southern Company's activity in the stock option program for 2017 is summarized below:

	Shares Subject to Option	Weighted Average Exercise Price
	(in millions)
Outstanding at December 31, 2016	24.6	$	41.28
Exercised	6.0	40.03
Cancelled	—	39.90
Outstanding and Exercisable at December 31, 2017	18.6	$	41.68

Assumptions used in the pricing model and the weighted average grant-date fair value of performance share award units granted

The following table shows the assumptions used in the pricing model and the weighted average grant-date fair value of performance share award units granted:

Year Ended December 31	2017	2016	2015
Expected volatility	15.6%	15.0%	12.9%
Expected term (in years)	3	3	3
Interest rate	1.4%	0.8%	1.0%
Weighted average grant-date fair value	$49.08	$45.06	$46.38

Earnings per share

Shares used to compute diluted EPS were as follows:

	Average Common Stock Shares
	2017	2016	2015
	(in millions)
As reported shares	1,000	951	910
Effect of options and performance share award units	8	7	4
Diluted shares	1,008	958	914