Discontinued Operations, Assets Held for Sale and Asset Impairments Sale - Components of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) Income from discontinued operations	$ (98.8)	$ (2.9)	$ (97.6)	$ 0
(Benefit) Provision for income taxes	(36.9)	(1.4)	(38.2)	(2.4)
Loss on discontinued operations, net	(61.9)	(1.5)	(59.4)	2.4
TECO Coal and TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues	101.6	123.7	328.3	370.0
(Loss) Income from operations	(0.4)	(2.9)	0.8	0
(Loss) on impairment	(98.4)	0	(98.4)	0
(Loss) Income from discontinued operations	(98.8)	(2.9)	(97.6)	0
(Benefit) Provision for income taxes	(36.9)	(1.4)	(38.2)	(2.4)
Loss on discontinued operations, net	$ (61.9)	$ (1.5)	$ (59.4)	$ 2.4