Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 0	$ 1	$ 0	$ 1
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	1	2	2	3
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	4	9	8
Interest cost	8	9	17	18
Expected return on assets	(13)	(13)	(27)	(27)
Amortization of:
Amortization of actuarial loss (gain)	1	1	3	2
Settlement cost	0	2	0	2
Net periodic benefit cost	1	3	2	3
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	2	3	4
Expected return on assets	0	0	0	0
Amortization of:
Amortization of actuarial loss (gain)	0	(1)	(1)	(1)
Settlement cost	0	0	0	0
Net periodic benefit cost	$ 1	$ 1	$ 2	$ 3