Derivatives - Energy-Related and Interest Rate Derivatives (Details) BTU in Millions, $ in Millions, MMBTU in Billions	6 Months Ended
Jun. 30, 2017 USD ($) MMBTU BTU
Interest Rate Contract
Interest rate derivatives
Notional Amount	$ 3,900
Fair Value Gain (Loss) at June 30, 2017	$ (11)
Southern Company \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| BTU	472
Longest Hedge Date	2021
Longest Non-Hedge Date	2024
Southern Company \| Interest Rate Contract \| 2017-08-01 \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	1.30%
Fair Value Gain (Loss) at June 30, 2017	$ 0
Southern Company \| Interest Rate Contract \| 2017-08-01 \| London Interbank Offered Rate (LIBOR) \| Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.17%
Southern Company \| Interest Rate Contract \| 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 June 30, 2017	$ 1
Southern Company \| Interest Rate Contract \| 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 Contract \| 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 June 30, 2017	$ (14)
Southern Company \| Interest Rate Contract \| 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 \| BTU	70
Longest Hedge Date	2020
GEORGIA POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| BTU	160
Longest Hedge Date	2020
GEORGIA POWER CO \| Interest Rate Contract \| 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 June 30, 2017	$ 0
GEORGIA POWER CO \| Interest Rate Contract \| 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 Contract \| 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 June 30, 2017	$ (2)
GEORGIA POWER CO \| Interest Rate Contract \| 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 Contract \| 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 June 30, 2017	$ 1
GEORGIA POWER CO \| Interest Rate Contract \| 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 \| BTU	35
Longest Hedge Date	2020
MISSISSIPPI POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| BTU	41
Longest Hedge Date	2021
MISSISSIPPI POWER CO \| Interest Rate Contract \| 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 June 30, 2017	$ 3
SOUTHERN POWER CO \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| BTU	25
Longest Hedge Date	2017
SOUTHERN Co GAS \| Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu \| BTU	141
Longest Hedge Date	2019
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	3.5
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	3.4

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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