Accounting for Derivative Instruments and Hedging Activities - Derivatives Designated as Cash Flow Hedges (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Current assets	$ 8.2	$ 9.7
Long-term assets	0.5	0.3
Total assets	8.7	10.0
Current liabilities	0.2	0.1
Long-term liabilities	0.1	0.2
Total liabilities	0.3	0.3
Tampa Electric Company [Member]
Derivatives, Fair Value [Line Items]
Current assets	8.1	9.5
Long-term assets	0.5	0.3
Current liabilities	0.2	0
Long-term liabilities	0.1	0.2
Natural Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current assets	8.1	9.5
Long-term assets	0.5	0.3
Total assets	8.6	9.8
Current liabilities	0.2	0
Long-term liabilities	0.1	0.2
Total liabilities	0.3	0.2
Natural Gas Derivatives [Member] | Tampa Electric Company [Member]
Derivatives, Fair Value [Line Items]
Current assets	8.1	9.5
Long-term assets	0.5	0.3
Total assets	8.6	9.8
Current liabilities	0.2	0
Long-term liabilities	0.1	0.2
Total liabilities	0.3	0.2
Diesel Fuel Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current assets	0.1	0.2
Long-term assets	0	0
Total assets	0.1	0.2
Current liabilities	0	0.1
Long-term liabilities	0	0
Total liabilities	$ 0	$ 0.1