Disclosures about Derivative Instruments and Hedging Activities (Details 2) (USD $)	3 Months Ended	9 Months Ended
	Dec. 31, 2011	Sep. 30, 2012
Derivative instruments and hedging activities
Maximum borrowing capacity, to construct Plant Vogtle Units No.3 and No. 4, with the Department of Energy		$ 3,057,000,000
Purchased amount of derivative instrument		43,070,000
LIBOR swaptions
Derivative instruments and hedging activities
Purchased amount of derivative instrument	100,000,000
Hedged amount of the expected Department of Energy-guaranteed loan	2,200,000,000
Variable rate basis		LIBOR
Weighted average fixed rate (as a percent)		4.17%
Fair value of assets	69,446,000	29,921,000
Funds posted as collateral by the counterparties	43,070,000	7,810,000
Carrying amount of derivative assets	26,376,000	22,111,000
Notional Dollar Amount		2,179,204,000
LIBOR swaptions | 2013
Derivative instruments and hedging activities
Notional Dollar Amount		754,452,000
LIBOR swaptions | 2014
Derivative instruments and hedging activities
Notional Dollar Amount		563,425,000
LIBOR swaptions | 2015
Derivative instruments and hedging activities
Notional Dollar Amount		470,625,000
LIBOR swaptions | 2016
Derivative instruments and hedging activities
Notional Dollar Amount		310,533,000
LIBOR swaptions | 2017
Derivative instruments and hedging activities
Notional Dollar Amount		80,169,000
LIBOR swaptions | Minimum
Derivative instruments and hedging activities
Fixed interest rates above LIBOR swap rates (as a percent)		1.50%
Collateral thresholds range		0
LIBOR swaptions | Maximum
Derivative instruments and hedging activities
Fixed interest rates above LIBOR swap rates (as a percent)		2.50%
Collateral thresholds range		$ 10,000,000