Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative assets	$ 0	$ 200,000
Derivative liabilities	23,100,000	26,200,000
Cash collateral posted with or received from any counterparties	0	0
Net pretax gain (loss) expected to be reclassified from regulatory assets or liabilities, next 12 months	(22,300,000)
Tampa Electric Company [Member]
Derivative [Line Items]
Derivative assets	0	0
Derivative liabilities	23,000,000	26,200,000
Cash collateral posted with or received from any counterparties	0	$ 0
Net pretax gain (loss) expected to be reclassified from regulatory assets or liabilities, next 12 months	$ (22,200,000)
Natural Gas Contracts [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Feb. 28, 2018
Natural Gas Contracts [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Feb. 28, 2018