Discontinued Operations and Asset Impairments - Components of Discontinued Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ 0.2	$ (9.6)
Provision (benefit) from income taxes	0.1	(3.8)
Income (loss) from discontinued operations, net	0.1	(5.8)
TECO Coal [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues	0.0	72.7
Loss from operations	0.0	(9.5)
Income (loss) from discontinued operations	0.2	(9.5)
TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Loss from operations	0.0	(0.1)
Income (loss) from discontinued operations	0.0	(0.1)
TECO Coal and TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision (benefit) from income taxes	$ 0.1	$ (3.8)