Accounting For Derivative Instruments And Hedging Activities (Derivatives Designated As Cash Flow Hedges) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Current assets	$ 1.3	[1]	$ 2.7	[1]
Long-term assets	0.2	[1]	0.2	[1]
Total assets	1.5	[1]	2.9	[1]
Current liabilities	29.5	[1]	27.2	[1]
Long-term liabilities	6.0	[1]	2.6	[1]
Total liabilities	35.5	[1]	29.8	[1]
Tampa Electric Co [Member] | Natural Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current assets	0		1.1
Long-term assets	0		0
Total assets	0		1.1
Current liabilities	29.5		27.2
Long-term liabilities	4.5		2.6
Total liabilities	34.0		29.8
Natural Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current assets	0		1.1
Long-term assets	0		0
Total assets	0		1.1
Current liabilities	29.5		27.2
Long-term liabilities	4.5		2.6
Total liabilities	34.0		29.8
Diesel Fuel Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current assets	1.3		1.6
Long-term assets	0.2		0.2
Total assets	1.5		1.8
Current liabilities	0		0
Long-term liabilities	1.5		0
Total liabilities	1.5		0
Tampa Electric Co [Member]
Derivatives, Fair Value [Line Items]
Current assets	0		1.1
Current liabilities	29.5		27.2
Long-term liabilities	$ 4.5		$ 2.6

[1] Amounts presented above are on a gross basis, with asset and liability positions netted by counterparty in accordance with accounting standards for derivatives and hedging.