Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Derivative [Line Items]
Collateral posted with or received from any counterparties	$ 0		$ 0
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	7,400,000	[1]	7,800,000	[1]
Diesel Fuel [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Dec. 31, 2014
Natural Gas Contracts [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Dec. 31, 2016
Tampa Electric Company [Member]
Derivative [Line Items]
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	7,300,000	[2]	7,800,000	[2]
Net pretax gain (loss) expected to be reclassified from regulatory assets or liabilities	(3,900,000)
Interest Rate Swap [Member]
Derivative [Line Items]
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	7,400,000		7,800,000
Interest Rate Swap [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Net loss related to cash flow hedges and interest rate swaps in AOCI, after tax	$ 7,300,000		$ 7,800,000

[1] Net of tax benefit of $4.7 million and $4.9 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively.

[2] Net of tax benefit of $4.6 million and $4.9 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively.