Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Unbilled revenues	$ 67.3		$ 81.1
Franchise fees and gross receipts taxes	27.9	$ 27.4
Tampa Electric Company [Member]
Summary Of Significant Accounting Policies [Line Items]
Unbilled revenues	56.8		$ 53.7
Franchise fees and gross receipts taxes	$ 27.9	$ 27.4