Regulatory - Regulatory Assets and Related Recovery Periods (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
Regulatory assets	$ 452.9	$ 451.8
TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	452.9	451.8
Clause recoverable [Member]
Regulatory Assets [Line Items]
Regulatory assets	47.0	76.8
Clause recoverable [Member] | TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	47.0	76.8
Components of rate base [Member]
Regulatory Assets [Line Items]
Regulatory assets	279.1	264.9
Components of rate base [Member] | TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	279.1	264.9
Regulatory tax asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	63.6
Regulatory tax asset [Member] | TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	63.6
Capital structure and other [Member]
Regulatory Assets [Line Items]
Regulatory assets	59.6	46.5
Capital structure and other [Member] | TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 59.6	$ 46.5