Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 0	$ 0
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	1	1
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4
Interest cost	9	9
Expected return on assets	(14)	(14)
Amortization of:
Amortization of actuarial loss (gain)	2	1
Net periodic benefit cost	1	0
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	2	2
Expected return on assets	0	0
Amortization of:
Amortization of actuarial loss (gain)	(1)	0
Net periodic benefit cost	$ 1	$ 2