Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Components Of Deferred Tax Assets And Liabilities [Line Items]
Stockholder's equity increment	$ 2.6
Valuation allowance	2.0	$ 4.6
TECO Coal [Member] | Discontinued Operations [Member]
Components Of Deferred Tax Assets And Liabilities [Line Items]
Valuation allowance	$ 1.0	$ 3.6