Accounting For Derivative Instruments And Hedging Activities (Energy Related Derivatives) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current regulatory assets	$ 83.2		$ 87.3
Long-term regulatory assets	351.1		364.5
Regulatory assets	434.3		451.8
Current regulatory liabilities	83.4		86.2
Long-term regulatory liabilities	654.1		647.8
Regulatory liabilities	737.5		734.0
Tampa Electric Co [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	83.2		87.3
Long-term regulatory assets	351.1		364.5
Regulatory assets	434.3		451.8
Current regulatory liabilities	83.4		86.2
Long-term regulatory liabilities	654.1		647.8
Regulatory liabilities	737.5		734.0
Energy Related Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	38.9	[1]
Long-term regulatory assets	2.6	[1]
Regulatory assets	41.5	[1]
Current regulatory liabilities	0.4	[1]
Long-term regulatory liabilities	0.1	[1]
Regulatory liabilities	0.5	[1]
Energy Related Derivatives [Member] | Tampa Electric Co [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	38.9	[1]
Long-term regulatory assets	2.6	[1]
Regulatory assets	41.5	[1]
Current regulatory liabilities	0.4	[1]
Long-term regulatory liabilities	0.1	[1]
Regulatory liabilities	$ 0.5	[1]

[1] Natural gas derivatives are deferred in accordance with accounting standards for regulated operations and all increases and decreases in the cost of natural gas supply are passed on to customers with the fuel recovery clause mechanism. As gains and losses are realized in future periods, they will be recorded as fuel costs in the Consolidated Condensed Statements of Income.