Income Taxes - Schedule of Income Taxes Calculated on Income before Income Taxes and Provision for Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
Income tax expense at the federal statutory rate of 35%	$ 134.3	$ 137.7	$ 112.4
State income tax, net of federal income tax	12.7	12.4	6.8
Equity portion of AFUDC	(0.9)	(0.4)	(0.7)
Valuation allowance	1.1	0	1.9
Depletion	(8.5)	(9.1)	(9.1)
Other	(0.9)	2.1	(1.7)
Total income tax expense from continuing operations	137.8	142.7	109.6
Total income tax expense	160.2	153.9	170.0
Income tax expense as a percent of income from continuing operations, before income taxes	35.90%	36.30%	34.10%
TAMPA ELECTRIC CO [Member]
Schedule Of Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
Income tax expense at the federal statutory rate of 35%	129.1	133.2	135.3
State income tax, net of federal income tax	13.2	13.6	13.6
Equity portion of AFUDC	(0.9)	(0.4)	(0.7)
Domestic production deduction	(0.4)	(1.5)	(3.2)
Other	0.7	0.5	(1.3)
Total income tax expense from continuing operations	141.7	145.4	143.7
Total income tax expense	$ 141.7	$ 145.4	$ 143.7
Income tax expense as a percent of income from continuing operations, before income taxes	38.40%	38.20%	37.20%