Employee Postretirement Benefits (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.50%
Contributions to pension plan			$ 20.1
Tampa Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.50%
Contributions to pension plan			15.7
Reclassification of regulatory assets to net income as part of periodic benefit expense	3.8		7.3
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.797%		4.797%
Net pension expense	6.6	4.7	12.4	9.7
Pension Benefits [Member] | Tampa Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.797%		4.797%
Net pension expense	5.0	3.1	9.2	6.7
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.744%		4.744%
Net pension expense	3.8	3.9	7.6	8.2
Other Postretirement Benefits [Member] | Tampa Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.744%		4.744%
Net pension expense	3.1	3.2	6.2	6.7
Corresponding Charge [Member]
Defined Benefit Plan Disclosure [Line Items]
Reclassification of AOCI to net income as part of periodic benefit expense	0.8		1.5
Regulatory Tax Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Reclassification of regulatory assets to net income as part of periodic benefit expense	$ 3.8		$ 7.3