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Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative assets	$ 300,000us-gaap_DerivativeAssets	$ 0us-gaap_DerivativeAssets
Derivative liabilities	40,800,000us-gaap_DerivativeLiabilities	42,700,000us-gaap_DerivativeLiabilities
Cash collateral posted with or received from any counterparties	0	0
Net pretax gain (loss) expected to be reclassified from regulatory assets or liabilities	(35,200,000)
Tampa Electric Company [Member]
Derivative [Line Items]
Derivative assets	300,000	0
Derivative liabilities	40,800,000	42,700,000
Cash collateral posted with or received from any counterparties	0	0
Net pretax gain (loss) expected to be reclassified from regulatory assets or liabilities	$ (35,200,000)
Natural Gas Contracts [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Mar. 31, 2017
Natural Gas Contracts [Member] \| Tampa Electric Company [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Mar. 31, 2017

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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