Accounting for Derivative Instruments and Hedging Activities - Effect of Hedging Instruments on Other Comprehensive Income and Income (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
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) on Derivatives Recognized in OCI	$ (0.2)	$ 0.7	$ (0.2)	$ 0.4
Amount of Gain/(Loss) Reclassified From AOCI Into Income	(0.3)	(0.1)	(0.6)	(0.7)
Tampa Electric Company [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified From AOCI Into Income	(0.3)	(0.2)	(0.5)	(0.7)
Diesel Fuel Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) on Derivatives Recognized in OCI	(0.2)	0.7	(0.2)	0.4
Location of Gain/(Loss) Reclassified From AOCI Into Income	Loss from discontinued operations	Loss from discontinued operations	Loss from discontinued operations	Loss from discontinued operations
Amount of Gain/(Loss) Reclassified From AOCI Into Income	0	0.1	(0.1)	0
Interest rate contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) on Derivatives Recognized in OCI	0	0	0	0
Location of Gain/(Loss) Reclassified From AOCI Into Income	Interest expense	Interest expense	Interest expense	Interest expense
Amount of Gain/(Loss) Reclassified From AOCI Into Income	(0.3)	(0.2)	(0.5)	(0.7)
Interest rate contracts [Member] | Tampa Electric Company [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified From AOCI Into Income	$ (0.3)	$ (0.2)	$ (0.5)	$ (0.7)