Regulatory - Regulatory Assets and Related Recovery Periods (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Regulatory Asset [Line Items]
Regulatory assets	$ 366.5	$ 327.4
Tampa Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory assets	334.6	327.4
Components of Rate Base [Member]
Regulatory Asset [Line Items]
Regulatory assets	199.3	185.6
Components of Rate Base [Member] | Tampa Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory assets	190.9	185.6
Clause Recoverable [Member]
Regulatory Asset [Line Items]
Regulatory assets	11.9	10.2
Clause Recoverable [Member] | Tampa Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory assets	10.6	10.2
Regulatory Tax Asset [Member]
Regulatory Asset [Line Items]
Regulatory assets	69.1	67.4
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory assets	68.6	67.4
Capital Structure and Other [Member]
Regulatory Asset [Line Items]
Regulatory assets	86.2	64.2
Capital Structure and Other [Member] | Tampa Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory assets	$ 64.5	$ 64.2