Derivatives - Energy-Related and Interest Rate Derivatives (Details) MMBTU in Millions, $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($) MMBTU
Interest rate derivatives
Interest rate derivatives
Notional Amount	$ 3,650
Fair Value Gain (Loss) at September 30, 2017	$ (19)
Southern Company \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	463
Longest Hedge Date	2021
Longest Non-Hedge Date	2024
Southern Company \| Interest rate derivatives \| 2020-06-01 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 300
Interest Rate Received	2.75%
Fair Value Gain (Loss) at September 30, 2017	$ 0
Southern Company \| Interest rate derivatives \| 2020-06-01 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.92%
Southern Company \| Interest rate derivatives \| 7/31/2021 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Fair Value Gain (Loss) at September 30, 2017	$ (19)
Southern Company \| Interest rate derivatives \| 7/31/2021 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.87%
ALABAMA POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	66
Longest Hedge Date	2020
GEORGIA POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	159
Longest Hedge Date	2021
GEORGIA POWER CO \| Interest rate derivatives \| 6/1/2018 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	5.40%
Fair Value Gain (Loss) at September 30, 2017	$ 0
GEORGIA POWER CO \| Interest rate derivatives \| 6/1/2018 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	4.02%
GEORGIA POWER CO \| Interest rate derivatives \| 12/1/2018 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 500
Interest Rate Received	1.95%
Fair Value Gain (Loss) at September 30, 2017	$ (2)
GEORGIA POWER CO \| Interest rate derivatives \| 12/1/2018 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.76%
GEORGIA POWER CO \| Interest rate derivatives \| 12/1/2019 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 200
Interest Rate Received	4.25%
Fair Value Gain (Loss) at September 30, 2017	$ 0
GEORGIA POWER CO \| Interest rate derivatives \| 12/1/2019 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	2.46%
GULF POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	28
Longest Hedge Date	2020
MISSISSIPPI POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	44
Longest Hedge Date	2021
MISSISSIPPI POWER CO \| Interest rate derivatives \| 3/1/2018 \| Cash Flow Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 900
Weighted Average Interest Rate Paid	0.79%
Fair Value Gain (Loss) at September 30, 2017	$ 2
SOUTHERN POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	13
Longest Hedge Date	2018
SOUTHERN Co GAS \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| MMBTU	153
Longest Hedge Date	2020
Longest Non-Hedge Date	2024
SOUTHERN Co GAS \| Energy-related, Natural Gas \| Long \| Derivatives not designated as hedging instruments
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume \| MMBTU	3,300
SOUTHERN Co GAS \| Energy-related, Natural Gas \| Short \| Derivatives not designated as hedging instruments
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume \| MMBTU	3,100

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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