Accounting for Derivative Instruments and Hedging Activities - Derivative Activity for Instruments Classified as Qualifying Cash Flow Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Asset/(Liability)	$ (0.3)	$ (0.2)	$ (0.3)	$ (0.2)
Amount of Gain/(Loss) Recognized in OCI	0.7	1.6	0.4	(4.5)
Amount of Gain/(Loss) Reclassified From AOCI Into Income	(0.1)	(0.1)	(0.7)	(0.3)
Diesel Fuel Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Asset/(Liability)	(0.3)	(0.2)	(0.3)	(0.2)
Amount of Gain/(Loss) Recognized in OCI	0.7	1.6	0.4	0.4
Amount of Gain/(Loss) Reclassified From AOCI Into Income	0.1	0.1	0	0.3
Tampa Electric Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Asset/(Liability)	0	0	0	0
Amount of Gain/(Loss) Recognized in OCI	0		0	(4.9)
Amount of Gain/(Loss) Reclassified From AOCI Into Income	(0.2)		(0.7)	(0.6)
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Asset/(Liability)	0	0	0	0
Amount of Gain/(Loss) Recognized in OCI			0	(4.9)
Amount of Gain/(Loss) Reclassified From AOCI Into Income			(0.7)	(0.6)
Interest Rate Swap [Member] | Tampa Electric Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Asset/(Liability)	0	0	0	0
Amount of Gain/(Loss) Recognized in OCI			0	(4.9)
Amount of Gain/(Loss) Reclassified From AOCI Into Income			$ (0.7)	$ (0.6)