Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivatives And Hedging Activities [Line Items]
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	$ 9.2	$ 5.0
Net pretax losses expected to be reclassified from regulatory assets or liabilities	14.1
TAMPA ELECTRIC CO [Member]
Derivatives And Hedging Activities [Line Items]
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	8.7	4.6
Net pretax losses expected to be reclassified from regulatory assets or liabilities	$ 14.1