Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 0	$ 1
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	1	2
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4
Interest cost	9	6
Expected return on assets	(14)	(13)
Amortization of:
Actuarial loss (gain)	1	4
Net periodic benefit cost	0	1
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	2	1
Expected return on assets	0	0
Amortization of:
Actuarial loss (gain)	0	1
Net periodic benefit cost	$ 2	$ 2