Accounting for Derivative Instruments and Hedging Activities - Energy Related Derivatives (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Current regulatory assets	$ 34.3	$ 70.3
Long-term regulatory assets	293.1	382.6
Regulatory assets	327.4	452.9
Current regulatory liabilities	85.8	105.6
Long-term regulatory liabilities	631.4	631.4
Tampa Electric Company [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	34.3	70.3
Long-term regulatory assets	293.1	382.6
Regulatory assets	327.4	452.9
Current regulatory liabilities	85.8	105.6
Long-term regulatory liabilities	631.4	631.4
Regulatory liabilities	717.2	737.0
Energy Related Derivatives [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	0	14.1
Long-term regulatory assets	0.2	0.2
Regulatory assets	0.2	14.3
Current regulatory liabilities	9.5	0
Long-term regulatory liabilities	0.3	0.2
Regulatory liabilities	9.8	0.2
Energy Related Derivatives [Member] | Tampa Electric Company [Member]
Derivatives, Fair Value [Line Items]
Current regulatory assets	0	14.1
Long-term regulatory assets	0.2	0.2
Regulatory assets	0.2	14.3
Current regulatory liabilities	9.5	0
Long-term regulatory liabilities	0.3	0.2
Regulatory liabilities	$ 9.8	$ 0.2