Employee Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2024	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Reclassification of regulatory assets to net income as part of periodic benefit cost	$ 1	$ 1		$ 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	0	1		$ 0	1
Employer contributions				7	5
Pension Benefits [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 3
Pension Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	3		$ 2	3
Discount rate				5.27%
Employer contributions				$ 12	8
Pension Benefits [Member] | TECO Holdings [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 4
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	2		2	3
Other Postretirement Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 1	$ 1		$ 2	$ 3
Discount rate				5.28%