Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Income Tax Expense Benefit	$ 160.2	$ 153.9	$ 170.0
Actual cash paid for alternative minimum tax related to state income tax	7.2	9.4	5.5
Effective tax rate	35.00%	35.00%	35.00%
Use of operating loss carryforward	13.6	32.1	78.4
Federal and state (Florida) net operating losses (NOL's) carry forward	1,298.8
Deferred tax assets expiration date	2025 and 2028
General business credit	3.9
Deferred tax general business credits expiration date	2026 and 2031
Foreign tax credits	38.5
Tax credit carry forwards	211.8	196.1
Increased valuation allowance	6.7
Foreign tax credit valuation allowance	7.8
Valuation allowance expiration year	2013
Tax benefits, likelihood of being realized upon ultimate settlement	50.00%
Interest charges associated with uncertain tax positions	0.3	0.2	(1.1)
Interest accrued	0.9
Income tax examination period	1 year
TAMPA ELECTRIC CO [Member]
Income Taxes [Line Items]
Income Tax Expense Benefit	141.7	145.4	143.7
Effective tax rate	35.00%	35.00%	35.00%
Tax benefits, likelihood of being realized upon ultimate settlement	50.00%
Statutes of limitations	3
Income tax examination period	1 year
Minimum [Member]
Income Taxes [Line Items]
Effective tax rate	35.00%
Tax credit carry forwards	196.1
Statutes of limitations	3
Maximum [Member]
Income Taxes [Line Items]
Tax credit carry forwards	211.8
Statutes of limitations	4
State And Local Jurisdiction [Member]
Income Taxes [Line Items]
Federal and state (Florida) net operating losses (NOL's) carry forward	326.8
State capital loss valuation allowance	1.1
State capital loss carryforward deferred tax assets	$ 3.0