Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Tampa Electric Company [Member]	Sep. 30, 2013 Tampa Electric Company [Member]	Sep. 30, 2014 Tampa Electric Company [Member]	Sep. 30, 2013 Tampa Electric Company [Member]	Sep. 30, 2014 Unbilled Revenues [Member]	Dec. 31, 2013 Unbilled Revenues [Member]	Sep. 30, 2014 Unbilled Revenues [Member] Tampa Electric Company [Member]	Dec. 31, 2013 Unbilled Revenues [Member] Tampa Electric Company [Member]
Summary Of Significant Accounting Policies [Line Items]
Unbilled revenues									$ 61.0	$ 46.7	$ 53.3	$ 46.7
Franchise fees and gross receipts taxes	$ 31.7	$ 29.7	$ 86.7	$ 81.8	$ 31.7	$ 29.7	$ 86.7	$ 81.8