Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative assets	$ 2,200,000	$ 200,000
Derivative liabilities	1,700,000	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	500,000
Tampa Electric Company [Member]
Derivative [Line Items]
Derivative assets	1,500,000	0
Derivative liabilities	1,500,000	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	$ (100,000)
Natural Gas Contracts [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Sep. 30, 2018
Natural Gas Contracts [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Maximum length of time hedging in future cash flow	Sep. 30, 2018