Consolidated Statements of Capitalization (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Annual interest requirement	$ 1,700
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, shares issued (in shares)	1,000,000,000	1,000,000,000
Treasury shares (in shares)	1,000,000	900,000
Redeemable Preferred Stock, $100 par or stated value
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	475,115	809,325
Redeemable Preferred Stock, $1 par value
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, dividend rate	5.83%	5.83%
Redeemable cumulative preferred stock, shares authorized (in shares)	28,000,000	28,000,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	10,000,000	10,000,000
Redeemable Preferred Stock
Annual dividend requirement	$ 15	$ 15
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042
Fixed stated interest rate of debt obligation	5.50%
Pollution control revenue bonds - 4.55%
Fixed stated interest rate of debt obligation	4.55%	4.55%
Pollution control revenue bonds - variable rates (1.76% at 12/31/18) due 2022
Fixed stated interest rate of debt obligation	1.76%
Plant Daniel revenue bonds (7.13%) due 2021
Fixed stated interest rate of debt obligation	7.13%	7.13%
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Fixed stated interest rate of debt obligation		1.71%
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Fixed stated interest rate of debt obligation		1.71%
First mortgage bonds — 4.70% due 2019
Fixed stated interest rate of debt obligation	4.70%	4.70%
First mortgage bonds - 5.80% due 2023
Fixed stated interest rate of debt obligation	5.80%	5.80%
Alabama Power
Annual interest requirement	$ 330
Common stock, par value (in dollars per share)	$ 40	$ 40
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares outstanding (in shares)	30,537,500	30,537,500
Alabama Power | Cumulative preferred stock
Annual dividend requirement	$ 15
Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	3,850,000	3,850,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	475,115	475,115
Alabama Power | Redeemable Preferred Stock, $1 par value | Cumulative preferred stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, dividend rate	5.00%	5.00%
Redeemable cumulative preferred stock, shares authorized (in shares)	27,500,000	27,500,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	10,000,000	10,000,000
Alabama Power | Redeemable Preferred Stock, $25 stated value | Cumulative preferred stock
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Alabama Power | Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042
Fixed stated interest rate of debt obligation	5.50%	5.50%
Alabama Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.125%	5.125%
Alabama Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.375%	3.375%
Alabama Power | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	3.55%	3.55%
Georgia Power
Annual interest requirement	$ 356	$ 356
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	9,261,500	9,261,500
Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		2.29%
Georgia Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	4.25%	4.25%
Georgia Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	2.00%	2.00%
Georgia Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.40%	2.40%
Georgia Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	2.85%	2.85%
Georgia Power | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	5.75%	5.75%
Georgia Power | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.35%	2.35%
Mississippi Power
Fixed stated interest rate of debt obligation	7.13%
Annual interest requirement	$ 70	$ 70
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	1,244,139	1,244,139
Redeemable cumulative preferred stock, shares outstanding (in shares)	0	334,210
Common stock, shares authorized (in shares)	1,130,000	1,130,000
Common stock, shares outstanding (in shares)	1,121,000	1,121,000
Mississippi Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		3.05%
Mississippi Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.55%	5.55%
Mississippi Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.47%
Mississippi Power | Pollution control revenue bonds - 5.15% due 2028
Fixed stated interest rate of debt obligation	5.15%	5.15%
Mississippi Power | Plant Daniel revenue bonds (7.13%) due 2021
Fixed stated interest rate of debt obligation	7.13%	7.13%
Southern Company Gas
Annual interest requirement	$ 244	$ 244
Common stock, par value (in dollars per share)	$ 0.01	$ 10,000.00
Common stock, shares authorized (in shares)	100,000,000	100
Common stock, shares outstanding (in shares)	100	100
Southern Company Gas | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	3.50%	3.50%
Southern Company Gas | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.25%	5.25%
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Fixed stated interest rate of debt obligation		1.71%
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Fixed stated interest rate of debt obligation		1.71%
Southern Company Gas | First mortgage bonds — 4.70% due 2019
Fixed stated interest rate of debt obligation	4.70%	4.70%
Southern Company Gas | First mortgage bonds - 5.80% due 2023
Fixed stated interest rate of debt obligation	5.80%	5.80%
Minimum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%	4.20%
Minimum | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	1.50%	1.50%
Minimum | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	1.85%	1.85%
Minimum | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	2.00%	2.00%
Minimum | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.35%	2.35%
Minimum | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	1.00%	1.00%
Minimum | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	2.45%	0.00%
Minimum | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	1.63%	1.625%
Minimum | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.10%	2.10%
Minimum | Pollution control revenue bonds - 1.15% to 2.60% due 2023
Fixed stated interest rate of debt obligation	1.15%	1.15%
Minimum | Pollution control revenue bonds - 1.38% to 4.00% due 2025-2049
Fixed stated interest rate of debt obligation	1.40%	1.40%
Minimum | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.77%
Minimum | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.76%
Minimum | Pollution control revenue bonds - variable rates (1.70% to 1.87% at 12/31/18) due 2024 to 2053
Fixed stated interest rate of debt obligation		1.70%
Minimum | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	2.66%	2.66%
Minimum | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	5.00%	5.00%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		2.29%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.10%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.34%
Minimum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%	4.20%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.38%	2.38%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	2.80%	2.80%
Minimum | Alabama Power | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.76%	1.76%
Minimum | Alabama Power | Pollution control revenue bonds - 1.625% to 2.90% due 2034
Fixed stated interest rate of debt obligation	1.625%	1.625%
Minimum | Alabama Power | Pollution control revenue bonds - variable rates (1.70% to 1.80% at 12/31/18) due 2024-2038
Fixed stated interest rate of debt obligation	1.70%	1.70%
Minimum | Alabama Power | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.70%	3.70%
Minimum | Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	1.95%	1.95%
Minimum | Georgia Power | Long-term senior notes and debt maturing 2026-2043
Fixed stated interest rate of debt obligation	3.25%	3.25%
Minimum | Georgia Power | Pollution control revenue bonds - 1.55% to 4.00% due 2025 to 2049
Fixed stated interest rate of debt obligation	1.55%	1.55%
Minimum | Georgia Power | Pollution control revenue bonds - variable rates (1.77% to 1.78% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.77%
Minimum | Georgia Power | Pollution control revenue bonds - variable rates (1.70% to 1.83% at 12/31/18) due 2026-2052
Fixed stated interest rate of debt obligation	1.70%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	5.00%	5.00%
Minimum | Mississippi Power
Preferred stock, dividend rate	4.40%	4.40%
Minimum | Mississippi Power | Long-term senior notes and debt maturing 2028-2042
Fixed stated interest rate of debt obligation	3.95%	3.95%
Minimum | Mississippi Power | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.20%	2.20%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.50%	3.50%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.55%	8.55%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2025-2047
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Southern Company Gas | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	2.66%	2.66%
Maximum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	5.44%	5.44%
Maximum | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.55%	5.55%
Maximum | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	4.75%	4.75%
Maximum | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	9.10%	9.10%
Maximum | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.70%	8.70%
Maximum | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	5.75%	0.00%
Maximum | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	7.30%	7.30%
Maximum | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.35%	2.35%
Maximum | Pollution control revenue bonds - 1.15% to 2.60% due 2023
Fixed stated interest rate of debt obligation	2.60%	2.60%
Maximum | Pollution control revenue bonds - 1.38% to 4.00% due 2025-2049
Fixed stated interest rate of debt obligation	5.15%	5.15%
Maximum | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.23%
Maximum | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.87%
Maximum | Pollution control revenue bonds - variable rates (1.70% to 1.87% at 12/31/18) due 2024 to 2053
Fixed stated interest rate of debt obligation		1.87%
Maximum | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	6.58%	6.58%
Maximum | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	6.25%	6.25%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		3.05%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.50%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.91%
Maximum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.92%	4.92%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.95%	3.95%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	5.875%	5.875%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	6.125%	6.125%
Maximum | Alabama Power | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.87%	1.87%
Maximum | Alabama Power | Pollution control revenue bonds - 1.625% to 2.90% due 2034
Fixed stated interest rate of debt obligation	2.90%	2.90%
Maximum | Alabama Power | Pollution control revenue bonds - variable rates (1.70% to 1.80% at 12/31/18) due 2024-2038
Fixed stated interest rate of debt obligation	1.80%	1.80%
Maximum | Alabama Power | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.91%	3.91%
Maximum | Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Georgia Power | Long-term senior notes and debt maturing 2026-2043
Fixed stated interest rate of debt obligation	5.95%	5.95%
Maximum | Georgia Power | Pollution control revenue bonds - 1.55% to 4.00% due 2025 to 2049
Fixed stated interest rate of debt obligation	4.00%	4.00%
Maximum | Georgia Power | Pollution control revenue bonds - variable rates (1.77% to 1.78% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.78%
Maximum | Georgia Power | Pollution control revenue bonds - variable rates (1.70% to 1.83% at 12/31/18) due 2026-2052
Fixed stated interest rate of debt obligation	1.83%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Mississippi Power
Preferred stock, dividend rate	5.25%	5.25%
Maximum | Mississippi Power | Long-term senior notes and debt maturing 2028-2042
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Mississippi Power | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.23%	2.23%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	9.10%	9.10%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.70%	8.70%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2025-2047
Fixed stated interest rate of debt obligation	7.30%	7.30%
Maximum | Southern Company Gas | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	6.58%	6.58%