Contractual interest rate for funds borrowed, under the debt agreement.

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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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Long-Term Debt - Additional Information (Detail) - USD ($) $ in Millions				3 Months Ended
	Mar. 15, 2016	Mar. 15, 2012	Mar. 19, 2008	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, carrying amount				$ 3,573.0		$ 3,822.5
Estimated fair value				3,879.1		4,061.6
Purchase in lieu of redemption				250.0	$ 0.0
HCIDA Pollution Control Revenue Refunding Bonds [Member] \| Held Bonds [Member]
Debt Instrument [Line Items]
Purchase in lieu of redemption				232.6
Tampa Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt, carrying amount				2,245.3		2,245.0
Estimated fair value				$ 2,483.1		$ 2,433.3
Tampa Electric Company [Member] \| HCIDA Pollution Control Revenue Refunding Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, repurchase date	Mar. 15, 2016	Mar. 15, 2012	Mar. 19, 2008
Purchase in lieu of redemption			$ 86.0
Stated interest rate	2.00%	1.875%	5.00%