Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			44 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Unbilled revenues and Taxes, other than income [Line Items]
Equity method investment information	In certain circumstances this can result in the company consolidating entities in which it has less than a 50% equity investment and deconsolidating entities in which it has a majority equity interest
Restricted cash	$ 0	$ 8.7		$ 0
Percentage of original cost of depreciable property	3.80%	3.60%	3.60%
Depreciation expense	309.3	306.6	297.1
Allowance for funds used during construction rate				8.16%
Purchased power	105.3	125.9	179.6
Taxes, other than income	222.3	223.7	224.5
Minimum [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Discount rates used in estimating other self-insurance liabilities	2.60%	3.75%
Maximum [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Discount rates used in estimating other self-insurance liabilities	4.00%	4.75%
Unbilled revenues [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Unbilled revenues	49.0	50.2		49.0
Excise Taxes Franchise Fees and Gross Receipts [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Taxes, other than income	111.5	109.3	116.1
TECO Energy Source [Member]
Unbilled revenues and Taxes, other than income [Line Items]
TECO Energy Source	13.8	2.5	8.7
TECO Coal [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Shipping and Handling	9.0	16.6	27.3
TAMPA ELECTRIC CO [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Equity method investment information	In certain circumstances this can result in TEC consolidating entities in which it has less than a 50% equity investment and deconsolidating entities in which it has a majority equity interest
Percentage of original cost of depreciable property	3.80%	3.60%	3.60%
Depreciation expense	275.1	263.7	255.4
Allowance for funds used during construction rate				8.16%
Allowance for funds used during construction	4.1	1.6	3.0
Purchased power	105.3	125.9	179.6
Taxes, other than income	184.0	179.7	183.9
TAMPA ELECTRIC CO [Member] | Unbilled revenues [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Unbilled revenues	49.0	50.2		49.0
TAMPA ELECTRIC CO [Member] | Excise Taxes Franchise Fees and Gross Receipts [Member]
Unbilled revenues and Taxes, other than income [Line Items]
Taxes, other than income	$ 111.5	$ 109.3	$ 116.1