Discontinued Operations, Assets Held for Sale and Asset Impairments Sale - Components of Discontinued Operations (Parenthetical) (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 from discontinued operations	$ (98.8)	$ (2.9)	$ (97.6)	$ 0
(Benefit) Provision for income taxes	(36.9)	(1.4)	(38.2)	(2.4)
TECO Guatemala [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) Income from operations		(0.2)	5.0
Loss from discontinued operations		(0.2)	5.0
(Benefit) Provision for income taxes		$ (0.1)	$ 1.9

Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Tax effect allocated to a disposal group that is classified as a component of the entity reported as a separate component of income before extraordinary items. Includes the tax effects of the following: income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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