Employee Postretirement Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.25%
Contributions to pension plan			$ 26.5
Reclassification of AOCI to net income as part of periodic benefit expense	0.7		1.3
Reclassification of regulatory assets to net income as part of periodic benefit expense	2.7		5.2
Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.25%
Contributions to pension plan			21.5
Reclassification of regulatory assets to net income as part of periodic benefit expense	2.7		5.2
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.118%		5.118%
Pension Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.118%		5.118%
Contributions to pension plan			26.5
Net pension expense	3.9	5.6	7.7	10.9
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.096%		5.096%
Other Postretirement Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.096%		5.096%
Net pension expense	$ 2.6	$ 2.4	$ 5.2	$ 5.0