Common Stock and Stock Compensation - Textual Stock Options (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term for options outstanding	5 years
Weighted average remaining contractual term for options exercisable	0 years
Aggregate intrinsic value for options outstanding	$ 119,000,000
Aggregate intrinsic value for options exercisable	0
Total compensation cost for award recognized in income, tax benefit	4,000,000
Total intrinsic value of options exercised	64,000,000	$ 120,000,000	$ 48,000,000
Actual tax benefit for the tax deduction from stock option exercised	25,000,000	46,000,000	19,000,000
Cash received from issuance related to option exercise	$ 239,000,000	$ 448,000,000	$ 154,000,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Award Expiration Period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	600,000
Total compensation cost for award recognized in income	$ 25,000,000
Total compensation cost for award recognized in income, tax benefit	$ 10,000,000
ROE-based Portion Of The Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total performance share units granted	25.00%	25.00%	25.00%
EPS-based Portion Of The Performance Share Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total performance share units granted	20.00%	25.00%	25.00%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Award Expiration Period	10 years
TSR-based Portion Of The Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total performance share units granted	30.00%	50.00%	50.00%
ALABAMA POWER CO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 17,000,000
Total intrinsic value of options exercised	12,000,000	$ 21,000,000	$ 8,000,000
Actual tax benefit for the tax deduction from stock option exercised	5,000,000	8,000,000	3,000,000
Cash received from issuance related to option exercise	$ 0
ALABAMA POWER CO \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	58,001
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 49.21
Total compensation cost for award recognized in income	$ 3,000,000
Total compensation cost for award recognized in income, tax benefit	1,000,000
GEORGIA POWER CO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	30,000,000
Total intrinsic value of options exercised	13,000,000	18,000,000	9,000,000
Actual tax benefit for the tax deduction from stock option exercised	5,000,000	7,000,000	4,000,000
Cash received from issuance related to option exercise	$ 0
GEORGIA POWER CO \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	59,218
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 49.22
Total compensation cost for award recognized in income	$ 3,000,000
Total compensation cost for award recognized in income, tax benefit	1,000,000
GULF POWER CO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	3,000,000
Total intrinsic value of options exercised	2,000,000	3,000,000	2,000,000
Cash received from issuance related to option exercise	$ 0
GULF POWER CO \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	15,736
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 48.88
MISSISSIPPI POWER CO \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	13,260
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 49.22
MISSISSIPPI POWER CO \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 4,000,000
Total intrinsic value of options exercised	2,000,000	4,000,000	3,000,000
Actual tax benefit for the tax deduction from stock option exercised	1,000,000	$ 2,000,000	$ 1,000,000
Cash received from issuance related to option exercise	$ 0

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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.

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

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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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