Stock Compensation - Aggregate Intrinsic Value for Options Exercised (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 39
Aggregate intrinsic value for options exercisable	39
Intrinsic value of options exercised	9	$ 64	$ 120
Tax benefit of options exercised	2	25	46
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	5
Aggregate intrinsic value for options exercisable	5
Intrinsic value of options exercised	2	12	21
Tax benefit of options exercised	0	5	8
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	13
Aggregate intrinsic value for options exercisable	13
Intrinsic value of options exercised	2	13	18
Tax benefit of options exercised	0	5	7
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	1
Aggregate intrinsic value for options exercisable	1
Intrinsic value of options exercised	1	2	4
Tax benefit of options exercised	$ 0	$ 1	$ 2

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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-Publisher FASB
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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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-Publisher FASB
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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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