Derivatives - Foreign Currency Derivatives (Details) - 12 months ended Dec. 31, 2016 € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Fair Value Gain Loss	$ (14)
Foreign currency derivatives | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	1,241
Receive Notional | €		€ 1,100
Fair Value Gain Loss	(58)
Southern Power [Member] | Foreign currency derivatives | Maturity Date June 2022 [Member] | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain Loss	$ (34)
Southern Power [Member] | Foreign currency derivatives | Maturity Date June 2026 [Member] | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain Loss	$ (24)