Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 1	$ 2	$ 5	$ 7
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	2	3	7	8
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	3	14	14
Interest cost	6	5	18	16
Expected return on assets	(13)	(13)	(39)	(39)
Amortization of:
Actuarial loss (gain)	4	7	13	18
Settlement cost			1	0
Net periodic benefit cost	2	2	7	9
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	1	2
Interest cost	1	1	4	4
Expected return on assets	0	0	0	0
Amortization of:
Actuarial loss (gain)	1	1	1	1
Settlement cost			0	0
Net periodic benefit cost	$ 2	$ 3	$ 6	$ 7