Subsequent Event - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	7 Months Ended
	Feb. 15, 2013	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Oct. 25, 2011	Mar. 25, 2011
Subsequent Event [Line Items]
Letter of credit facility	$ 150.0	$ 675.0	$ 675.0	$ 675.0	$ 200.0
Amended credit facility interest rate	50 basis points
Total interest rate	52.5 basis points
Credit facility amended maturity date	Feb. 14, 2014
TAMPA ELECTRIC CO [Member]
Subsequent Event [Line Items]
Letter of credit facility	$ 150.0	$ 475.0	$ 475.0	$ 475.0	$ 200.0	$ 200.0
Amended credit facility interest rate	50 basis points
Total interest rate	52.5 basis points	15	25
Credit facility amended maturity date	Feb. 28, 2014