Employee Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Reclassification of regulatory assets to net income as part of periodic benefit cost	$ 0	$ 0	$ 2	$ 1
TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term EROA			7.05%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	0	$ 1	1
Employer contributions			10	10
Pension Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	0	$ 3	3
Discount rate			5.27%
Employer contributions			$ 16
Pension Benefits [Member] | TECO Holdings [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions				16
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	1	3	4
Other Postretirement Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 2	$ 2	$ 4	$ 5
Discount rate			5.28%