Discontinued Operations, Assets Held for Sale and Asset Impairments - Components of Discontinued Operations (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ (78.1)	$ 0.0	$ (87.7)	$ 1.2
Benefit from income taxes	(28.4)	(0.8)	(32.2)	(1.3)
Income (loss) on discontinued operations, net	(49.7)	0.8	(55.5)	2.5
TECO Coal [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues	76.1	120.6	148.8	226.7
Income (loss) from operations	0.5	0.0	(9.0)	(3.8)
Loss on impairment	(78.6)	0.0	(78.6)	0.0
Income (loss) from discontinued operations	(78.1)	0.0	(87.6)	(3.8)
TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Income (loss) from operations	0.0	0.0	(0.1)	5.0
Income (loss) from discontinued operations	0.0	0.0	(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	(78.1)	0.0	(87.7)	1.2
Benefit from income taxes	(28.4)	(0.8)	(32.2)	(1.3)
Income (loss) on discontinued operations, net	$ (49.7)	$ 0.8	$ (55.5)	$ 2.5