Fair Value Measurements (Recurring Fair Value Measures) (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	$ 1.5	$ 2.9
Fair Value, Liabilities	35.5	29.8
Diesel Fuel Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	1.5	1.8
Fair Value, Liabilities	1.5
Diesel Fuel Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0
Diesel Fuel Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	1.5	1.8
Fair Value, Liabilities	1.5
Diesel Fuel Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0
Tampa Electric Co [Member] | Natural Gas Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	34.0	29.8
Tampa Electric Co [Member] | Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Tampa Electric Co [Member] | Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	34.0	29.8
Tampa Electric Co [Member] | Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Natural Gas Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	34.0	29.8
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	34.0	29.8
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Tampa Electric Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Tampa Electric Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	34.0	29.8
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	1.5	2.9
Fair Value, Liabilities	35.5	29.8
Tampa Electric Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	0	0
Tampa Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets	0	1.1
Fair Value, Liabilities	$ 34.0	$ 29.8