Derivatives - Interest Rate Derivatives (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Notional Amount	$ 4,027
Fair Value Gain Loss	(14)
Maturity Date November 2025 [Member] | Cash Flow Hedges of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 80
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.32%
Interest Rate Received	3-month LIBOR
Hedge Maturity Date	Dec. 15, 2026
Fair Value Gain Loss	$ 0
Maturity Date March 2018 [Member] | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 900
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.79%
Interest Rate Received	1-month LIBOR
Hedge Maturity Date	Mar. 01, 2018
Fair Value Gain Loss	$ 3
Maturity Date August 2017 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 250
Notional Amount of Interest Rate Derivatives Interest Rate Received	1.30%
Interest Rate Received	3-month LIBOR + 0.17%
Basis Spread on Variable Rate	0.17%
Hedge Maturity Date	Aug. 15, 2017
Fair Value Gain Loss	$ 0
Maturity Date June 2018 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 250
Notional Amount of Interest Rate Derivatives Interest Rate Received	5.40%
Interest Rate Received	3-month LIBOR + 4.02%
Basis Spread on Variable Rate	4.02%
Hedge Maturity Date	Jun. 01, 2018
Fair Value Gain Loss	$ 0
Maturity Date December 2018 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 500
Notional Amount of Interest Rate Derivatives Interest Rate Received	1.95%
Interest Rate Received	3-month LIBOR + 0.76%
Basis Spread on Variable Rate	0.76%
Hedge Maturity Date	Dec. 01, 2018
Fair Value Gain Loss	$ (2)
Maturity Date December 2019 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 200
Notional Amount of Interest Rate Derivatives Interest Rate Received	4.25%
Interest Rate Received	3-month LIBOR + 2.46%
Basis Spread on Variable Rate	2.46%
Hedge Maturity Date	Dec. 01, 2019
Fair Value Gain Loss	$ 1
Maturity Date June 2020 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 300
Notional Amount of Interest Rate Derivatives Interest Rate Received	2.75%
Interest Rate Received	3-month LIBOR + 0.92%
Basis Spread on Variable Rate	0.92%
Hedge Maturity Date	Jun. 15, 2020
Fair Value Gain Loss	$ 1
Maturity Date June 2021 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Notional Amount of Interest Rate Derivatives Interest Rate Received	2.35%
Interest Rate Received	1-month LIBOR + 0.87%
Basis Spread on Variable Rate	0.87%
Hedge Maturity Date	Jul. 01, 2021
Fair Value Gain Loss	$ (18)
Georgia Power [Member]
Derivative [Line Items]
Notional Amount	950
Fair Value Gain Loss	(1)
Georgia Power [Member] | Maturity Date June 2018 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 250
Notional Amount of Interest Rate Derivatives Interest Rate Paid	5.40%
Interest Rate Received	3-month LIBOR + 4.02%
Basis Spread on Variable Rate	4.02%
Hedge Maturity Date	Jun. 01, 2018
Fair Value Gain Loss	$ 0
Georgia Power [Member] | Maturity Date December 2018 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 500
Notional Amount of Interest Rate Derivatives Interest Rate Paid	1.95%
Interest Rate Received	3-month LIBOR + 0.76%
Basis Spread on Variable Rate	0.76%
Hedge Maturity Date	Dec. 01, 2018
Fair Value Gain Loss	$ (2)
Georgia Power [Member] | Maturity Date December 2019 [Member] | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 200
Notional Amount of Interest Rate Derivatives Interest Rate Paid	4.25%
Interest Rate Received	3-month LIBOR + 2.46%
Basis Spread on Variable Rate	2.46%
Hedge Maturity Date	Dec. 01, 2019
Fair Value Gain Loss	$ 1
Gulf Power [Member] | Maturity Date December 2026 [Member] | Cash Flow Hedges of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 80
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.32%
Interest Rate Received	3-month LIBOR
Hedge Maturity Date	Dec. 01, 2026
Fair Value Gain Loss	$ 0
Mississippi Power [Member] | Maturity Date March 2018 [Member] | Cash Flow Hedges of Existing Debt | Interest rate derivatives
Derivative [Line Items]
Notional Amount	$ 900
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.79%
Fair Value Gain Loss	$ 3
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date October 2016 [Member]
Derivative [Line Items]
Term of contract	15 years
RE Tranquility Holdings, LLC [Member] | Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date January 2017 [Member]
Derivative [Line Items]
Hedge Maturity Date	Jan. 31, 2017
RE Roserock Holdings, LLC [Member] | Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date January 2017 [Member]
Derivative [Line Items]
Notional Amount	$ 47
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.21%
Interest Rate Received	3-month LIBOR
Fair Value Gain Loss	$ 1