Discontinued Operations, Assets Held for Sale and Asset Impairments - Components of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ (9.6)	$ 1.2
Benefit for income taxes	(3.8)	(0.5)
Income (loss) on discontinued operations, net	(5.8)	1.7
TECO Coal [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues	72.7	106.1
Income (loss) from operations	(9.5)	(3.8)
Income (loss) from discontinued operations	(9.5)	(3.8)
TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from operations	(0.1)	5.0
Income (loss) from discontinued operations	(0.1)	5.0
TECO Coal and TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	(9.6)	1.2
Benefit for income taxes	(3.8)	(0.5)
Income (loss) on discontinued operations, net	$ (5.8)	$ 1.7