Income Taxes - Schedule of Income Tax Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred income taxes
Amortization of investment tax credits	$ (0.3)	$ (0.4)	$ (0.4)
Total income tax expense	160.2	153.9	170.0
Income tax expense from continuing operations	137.8	142.7	109.6
Income tax expense from discontinued operations	22.4	11.2	60.4
TAMPA ELECTRIC CO [Member]
Current income taxes
Current income taxes, Federal	(19.5)	(30.7)	60.1
Current income taxes, State	5.6	2.9	13.6
Deferred income taxes
Deferred income taxes, Federal	141.2	155.6	63.0
Deferred income taxes, State	14.7	18.0	7.4
Amortization of investment tax credits	(0.3)	(0.4)	(0.4)
Total income tax expense	141.7	145.4	143.7
Income tax expense from continuing operations	141.7	145.4	143.7
Continuing Operations [Member]
Current income taxes
Current income taxes, Federal	15.7	0	5.7
Current income taxes, State	1.1	0.9	(5.2)
Deferred income taxes
Deferred income taxes, Federal	102.9	124.0	93.9
Deferred income taxes, State	18.4	18.2	15.6
Amortization of investment tax credits	(0.3)	(0.4)	(0.4)
Discontinued Operations [Member]
Current income taxes
Current income taxes, Federal	0	0	0
Foreign	6.8	7.4	7.0
Current income taxes, State	0	0	0
Deferred income taxes
Deferred income taxes, Federal	14.9	4.4	53.5
Foreign	0	(0.3)	0
Deferred income taxes, State	$ 0.7	$ (0.3)	$ (0.1)