Derivatives - Energy-Related and Interest Rate Derivatives (Details) BTU in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) BTU
Interest Rate Contract [Member]
Interest rate derivatives
Notional Amount	$ 3,980
Fair Value Gain (Loss) at March 31, 2017	$ (18)
Southern Company [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	503
Longest Hedge Date	2021
Longest Non-Hedge Date	2024
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date August 2017 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	1.30%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date August 2017 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.17%
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date June 2020 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 300
Interest Rate Received	2.75%
Fair Value Gain (Loss) at March 31, 2017	$ 1
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date June 2020 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.92%
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date July 2021 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Fair Value Gain (Loss) at March 31, 2017	$ (21)
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date July 2021 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.87%
Alabama Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	71
Longest Hedge Date	2020
Georgia Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	155
Longest Hedge Date	2020
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date June 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	5.40%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date June 2018 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	4.02%
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 500
Interest Rate Received	1.95%
Fair Value Gain (Loss) at March 31, 2017	$ (3)
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2018 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.76%
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2019 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 200
Interest Rate Received	4.25%
Fair Value Gain (Loss) at March 31, 2017	$ 1
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2019 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	2.46%
Gulf Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	42
Longest Hedge Date	2020
Gulf Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2026 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivatives
Notional Amount	$ 80
Weighted Average Interest Rate Paid	2.32%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Mississippi Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	37
Longest Hedge Date	2021
Mississippi Power [Member] | Interest Rate Contract [Member] | Maturity Date March 2018 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 900
Weighted Average Interest Rate Paid	0.79%
Fair Value Gain (Loss) at March 31, 2017	$ 4
Southern Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	21
Longest Hedge Date	2017
Longest Non-Hedge Date	2017
Southern Company Gas [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	177
Longest Hedge Date	2019
Longest Non-Hedge Date	2024
Southern Company Gas [Member] | Energy-related, Natural Gas [Member] | Long [Member] | Not Designated as Hedging Instrument [Member]
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | BTU	3,400
Southern Company Gas [Member] | Energy-related, Natural Gas [Member] | Short [Member] | Not Designated as Hedging Instrument [Member]
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | BTU	3,200