Regulatory - Regulatory Assets and Related Recovery Periods (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory assets	$ 411.4	$ 452.9
Tampa Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	411.4	452.9
Clause Recoverable [Member]
Regulatory Assets [Line Items]
Regulatory assets	18.6	47.0
Clause Recoverable [Member] | Tampa Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	18.6	47.0
Components of Rate Base [Member]
Regulatory Assets [Line Items]
Regulatory assets	266.7	279.1
Components of Rate Base [Member] | Tampa Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	266.7	279.1
Regulatory Tax Asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	67.2
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	67.2
Capital Structure and Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	58.9	59.6
Capital Structure and Other [Member] | Tampa Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 58.9	$ 59.6