Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details) (USD $)	12 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2003	Jul. 15, 2012	Apr. 15, 2012	Sep. 30, 2008 Swaptions	Sep. 30, 2005 Swaptions
Derivative
Amount of gain (loss) recognized in income on derivatives	$ 0
Unrealized gain (loss) on derivatives	0		0
Number of swaption transactions prior to 2006										4
Number of counterparties that exercised their rights prior to 2009									3
Face amount						1,000,000,000
Proceeds from issuance of swaption						175,000,000
Interest rate								8.25%
Notional amount							1,000,000,000
Payments for (proceeds from) call monetization	60,000,000		0		0
FTP transaction limit	130,000,000
Maximum hedge volume	75.00%
Market value limitation of outstanding construction materials hedging transactions	100,000,000
Portfolio value at risk limit for foreign currency transactions	5,000,000
Coal Contract Derivatives
Derivative
Maximum number of years left on the derivative terms	6 years
Number of contracts	23		38
Notional amount	46,000,000		66,000,000
Fair value	(267,000,000)		239,000,000
Interest Rate Swaption
Derivative
Amount of gain (loss) recognized in income on derivatives	0	[1]	0	[1]
Unrealized losses on investments	168,000,000		365,000,000
Realized gains (losses)	0		0
Interest Rate Swap
Derivative
Amount of gain (loss) recognized in income on derivatives	0	[1]	0	[1]
Commodity Contract Derivatives
Derivative
Amount of gain (loss) recognized in income on derivatives	(22,000,000)	[1]	(27,000,000)	[1]
Fair value	(267,000,000)		239,000,000
Commodity Derivatives Under Financial Trading Program
Derivative
Amount of gain (loss) recognized in income on derivatives	(342,000,000)	[1]	(145,000,000)	[1]
Fair value	(229,000,000)	[2]	(234,000,000)	[2]
Natural Gas Contract Derivatives
Derivative
Maximum number of years left on the derivative terms	3 years
Number of contracts	25		13
Notional amount	51,000,000		5,000,000
Fair value	$ 0		$ 0
Futures and options contracts
Derivative
Remaining terms	1 year
Swap contracts
Derivative
Remaining terms	6 years

[1] All of TVA's derivative instruments that do not receive hedge accounting treatment have unrealized gains (losses) that would otherwise be recognized in income but instead are deferred as regulatory assets and liabilities. As such, there was no related gain (loss) recognized in income for these unrealized gains (losses) for theyears ended 2012 and 2011.

[2] The September 30, 2012, and September 30, 2011 balances in the Derivatives Under Financial Trading Program table show all open derivative positions in the FTP.