Derivatives - Energy-Related and Interest Rate Derivatives (Details) BTU in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) BTU
Interest Rate Contract [Member]
Interest rate derivatives
Notional Amount	$ 2,657
Fair Value Gain (Loss) at September 30, 2016	$ 12
Southern Company [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	540
Longest Hedge Date	2020
Longest Non-Hedge Date	2022
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 September 30, 2016	$ 1
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 September 30, 2016	$ 9
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%
Alabama Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	75
Longest Hedge Date	2020
Georgia Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	148
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 September 30, 2016	$ 2
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 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 September 30, 2016	$ 5
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%
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 September 30, 2016	$ 2
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%
Gulf Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	57
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 September 30, 2016	$ (6)
Mississippi Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	37
Longest Hedge Date	2020
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 September 30, 2016	$ (1)
Southern Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	9
Longest Hedge Date	2017
Longest Non-Hedge Date	2016
Southern Power [Member] | Interest Rate Contract [Member] | Maturity Date October 2016 Number One [Member] | Not Designated as Hedging Instrument [Member]
Interest rate derivatives
Notional Amount	$ 65
Weighted Average Interest Rate Paid	2.50%
Fair Value Gain (Loss) at September 30, 2016	$ 0
Southern Power [Member] | Interest Rate Contract [Member] | Maturity Date October 2016 Number Two [Member] | Not Designated as Hedging Instrument [Member]
Interest rate derivatives
Notional Amount	$ 47
Weighted Average Interest Rate Paid	2.21%
Fair Value Gain (Loss) at September 30, 2016	$ 0
Southern Power [Member] | Interest Rate Contract [Member] | Maturity Date October 2016 [Member] | Not Designated as Hedging Instrument [Member]
Interest rate derivatives
Derivative term	15 years
Southern Power [Member] | Interest Rate Contract [Member] | Maturity Date November 2016 [Member] | Not Designated as Hedging Instrument [Member]
Interest rate derivatives
Notional Amount	$ 65
Weighted Average Interest Rate Paid	2.21%
Fair Value Gain (Loss) at September 30, 2016	$ 0
Derivative term	12 years
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	3,200
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	2,900