Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 1	$ 3
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	2	2
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5
Interest cost	6	5
Expected return on assets	(13)	(13)
Amortization of:
Actuarial loss (gain)	4	6
Net periodic benefit cost	1	3
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on assets	0	0
Amortization of:
Actuarial loss (gain)	1	1
Net periodic benefit cost	$ 2	$ 2