Asset Retirement Obligations - Schedule of Asset Retirement Obligations (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation [Line Items]
Other asset retirement obligations	$ 0.3	$ (1.1)
Other [Member]
Asset Retirement Obligation [Line Items]
Other asset retirement obligations	$ 0.3	0.2
TECO Coal [Member] | Discontinued Operations [Member]
Asset Retirement Obligation [Line Items]
Other asset retirement obligations		$ (1.3)