Variable Interest Entities - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) MW	Mar. 31, 2015 USD ($)
Long Term Contract For Purchase Of Electric Power [Line Items]
Purchased power | $	$ 14.4	$ 17.1
Tampa Electric Company [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Purchased power | $	14.4	17.1
Power Purchase Agreements [Member] | Variable Interest Entity Not Primary Beneficiary [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Purchased power | $	12.6	5.4
Power Purchase Agreements [Member] | Variable Interest Entity Not Primary Beneficiary [Member] | Tampa Electric Company [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Purchased power | $	$ 12.6	$ 5.4
Minimum [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Multiple PPAs range | MW	117
Minimum [Member] | Tampa Electric Company [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Multiple PPAs range | MW	117
Maximum [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Multiple PPAs range | MW	250
Maximum [Member] | Tampa Electric Company [Member]
Long Term Contract For Purchase Of Electric Power [Line Items]
Multiple PPAs range | MW	250