Fair Value Measurements - Schedule of Recurring Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	$ 0.2	$ 10.0
Total Swap Liabilities	5.7	0.3
Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Natural Gas Derivatives [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Diesel Fuel Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	0.2
Total Swap Liabilities	0.1	0.1
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.2
Total Swap Liabilities	5.7
Fair Value, Measurements, Recurring [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.2
Total Swap Liabilities	5.7
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1
Total Swap Liabilities	5.6
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	0
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 1 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1
Total Swap Liabilities	5.6
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 2 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1	9.8
Total Swap Liabilities	5.6	0.2
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	0
Fair Value, Measurements, Recurring [Member] | Natural Gas Derivatives [Member] | Level 3 [Member] | Tampa Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0	0
Total Swap Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Diesel Fuel Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1
Total Swap Liabilities	0.1
Fair Value, Measurements, Recurring [Member] | Diesel Fuel Derivatives [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	0
Fair Value, Measurements, Recurring [Member] | Diesel Fuel Derivatives [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0.1
Total Swap Liabilities	0.1
Fair Value, Measurements, Recurring [Member] | Diesel Fuel Derivatives [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Swap Assets	0
Total Swap Liabilities	$ 0