Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost		$ 0	$ 1	$ 1	$ 5
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost		1	2	4	7
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		3	5	11	14
Interest cost		8	6	26	18
Expected return on assets		(13)	(13)	(40)	(39)
Amortization of:
Actuarial loss (gain)		2	4	4	13
Settlement cost	[1]			2	1
Net periodic benefit cost		0	2	3	7
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	0	0	1
Interest cost		2	1	6	4
Expected return on assets		0	0	0	0
Amortization of:
Actuarial loss (gain)		0	1	(1)	1
Settlement cost	[1]			0	0
Net periodic benefit cost		$ 2	$ 2	$ 5	$ 6

[1] Represents TEC's SERP and Restoration Plan settlement charges as a result of the prior retirements of certain executives.