Employee Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jan. 01, 2015
Defined Benefit Plan Disclosure [Line Items]
Reclassification of AOCI to net income as part of periodic benefit expense		$ 0.2		$ 2.4
Reclassification of regulatory assets to net income as part of periodic benefit expense		2.6	$ 2.7	7.8	$ 7.9
Accumulated Other Comprehensive Income Defined Benefit Plans Amortization Period Increase Decrease			0.7		2.0
TECO Coal [Member]
Defined Benefit Plan Disclosure [Line Items]
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		$ 2.3	2.6	$ 7.0	7.8
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA				7.00%
Discount rate		4.256%		4.256%
Employer contributions				$ 55.0	47.5
Net pension expense		$ 7.2	5.3	$ 19.0	15.8
Pension Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate		4.256%		4.256%
Employer contributions				$ 43.9	38.2
Net pension expense		$ 3.3	3.6	10.1	11.3
Other Postretirement Benefits Florida-Based Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate						4.206%
Other Postretirement Benefits, NMGC Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate						4.243%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net pension expense		2.0	3.3	6.0	9.7
Other Postretirement Benefits [Member] | New Mexico Gas Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions				2.7
Other Postretirement Benefits [Member] | Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate						4.206%
Net pension expense		$ 1.4	$ 2.6	$ 4.3	$ 7.8
SERP [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 43.4
SERP [Member] | Tampa Electric Company [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 14.9