Employee Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jan. 01, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Reclassification of AOCI to net income as part of periodic benefit expense	$ 1.4		$ 2.2
Reclassification of regulatory assets to net income as part of periodic benefit expense	3.0	$ 2.7	5.2	$ 5.2
Accumulated Other Comprehensive Income Defined Benefit Plans Amortization Period Increase Decrease		0.7		1.3
TECO Coal [Member]
Defined Benefit Plan Disclosure [Line Items]
Black lung liability	25.0		25.0			$ 24.7
Expenses related to black lung liability	$ 0.0	0.0	0.0	0.0
Settlement charge, related to unfunded black lung obligations			7.7
Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA	7.00%
Reclassification of regulatory assets to net income as part of periodic benefit expense	$ 2.8	2.7	$ 4.7	5.2
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.00%
Discount rate	4.256%		4.256%
Employer contributions			$ 24.5	26.5
Net pension expense	$ 7.4	5.4	$ 11.8	10.5
Pension Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.256%		4.256%
Employer contributions			$ 18.5	21.5
Net pension expense	$ 4.2	3.9	6.8	7.7
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate					4.206%
Net pension expense	2.0	3.2	4.0	6.4
Other Postretirement Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate					4.206%
Net pension expense	$ 1.5	$ 2.6	$ 2.9	$ 5.2