Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 3	$ 2	$ 4	$ 5
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	3	3	5	5
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6	9	11
Interest cost	6	6	12	11
Expected return on assets	(13)	(13)	(26)	(26)
Amortization of:
Actuarial loss (gain)	5	5	9	11
Settlement cost	1	0	1	0
Net periodic benefit cost	4	4	5	7
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1	1
Interest cost	2	2	3	3
Expected return on assets	0	0	0	0
Amortization of:
Actuarial loss (gain)	(1)	(1)	0	0
Settlement cost	0	0	0	0
Net periodic benefit cost	$ 2	$ 2	$ 4	$ 4