Employee Postretirement Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013 Tampa Electric Company [Member]	Sep. 30, 2013 Tampa Electric Company [Member]	Sep. 30, 2013 Pension Benefits [Member]	Sep. 30, 2013 Pension Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2012 Pension Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2013 Pension Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2012 Pension Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2013 Other Postretirement Benefits [Member]	Sep. 30, 2013 Other Postretirement Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2013 Other Postretirement Benefits [Member] Tampa Electric Company [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member] Tampa Electric Company [Member]	Jun. 30, 2013 SERP [Member]	Jun. 30, 2013 SERP [Member] Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA		7.50%		7.50%
Discount rate					4.196%	4.196%		4.196%		4.18%	4.18%		4.18%		4.96%	4.96%
Contributions to pension plan		$ 32.9		$ 26.1
Reclassification of AOCI to net income as part of periodic benefit expense	1.0	3.2
Reclassification of regulatory assets to net income as part of periodic benefit expense	4.1	12.3	4.1	12.3
Net pension expense						$ 5.4	$ 4.5	$ 16.3	$ 13.7		$ 2.5	$ 3.1	$ 7.5	$ 9.3