Subsequent Events (Details) (USD $) In Millions	9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 $200 Million Bank Credit Facility Amendment [Member]	Oct. 25, 2011 $200 Million Bank Credit Facility Amendment [Member]	Sep. 30, 2011 Tampa Electric Co [Member] $325 Million Bank Credit Facility Amendment [Member]	Oct. 25, 2011 Tampa Electric Co [Member] $325 Million Bank Credit Facility Amendment [Member]	Sep. 30, 2011 Tampa Electric Co [Member]	Dec. 31, 2010 Tampa Electric Co [Member]
Subsequent Event [Line Items]
Outstanding credit facilities	$ 0.7	$ 7.4		$ 200.0		$ 325.0	$ 0.7	$ 0.7
Credit facility initial maturity date			May 9, 2012		May 9, 2012
Credit facility amended maturity date			Oct. 25, 2016		Oct. 25, 2016
Amended credit facility interest rate			equal to a margin plus the higher of the JPMorgan Chase Bank's prime rate, the federal funds rate plus 50 basis points, or the London interbank deposit rate plus 1.00%		equal to a margin plus the higher of Citibank's prime rate, the federal funds rate plus 50 basis points, or the London interbank deposit rate plus 1.00%
Increase to commitments on credit facility	50		100		175
Letter of credit facility			$ 200		$ 200		$ 50