Fair Value Measurements - Schedule of Recurring Fair Value Measures (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	$ 0.2	$ 0.9
Total Swap Liabilities	15.2	67.0
TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Natural Gas Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Natural Gas Derivatives [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Diesel Fuel Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0.9
Total Swap Liabilities	0.9	1.2
Level 1 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 1 [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 1 [Member] | Natural Gas Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 1 [Member] | Natural Gas Derivatives [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 1 [Member] | Diesel Fuel Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 2 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0.9
Total Swap Liabilities	15.2	67.0
Level 2 [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Level 2 [Member] | Natural Gas Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Level 2 [Member] | Natural Gas Derivatives [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0.2	0
Total Swap Liabilities	14.3	65.8
Level 2 [Member] | Diesel Fuel Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0.9
Total Swap Liabilities	0.9	1.2
Level 3 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 3 [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 3 [Member] | Natural Gas Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 3 [Member] | Natural Gas Derivatives [Member] | TAMPA ELECTRIC CO [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Level 3 [Member] | Diesel Fuel Derivatives [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	$ 0	$ 0