Employee Postretirement Benefits - Schedule of Change in Benefit Obligation (Detail) - TECO Energy [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Pension Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year		$ 678		$ 666
Service cost		17		15		$ 18
Interest cost		35		35		23
Plan participants’ contributions		0		0
Benefits paid		(57)		(59)
Actuarial loss (gain)		1		27
Plan amendments		0		0
Plan settlement	[1]	0		(6)
Benefit obligation at end of year		674		678		666
Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	[2]	132		142
Service cost	[3]	1	[2]	1	[2]	2
Interest cost	[3]	7	[2]	7	[2]	5
Plan participants’ contributions	[2]	4		4
Benefits paid	[2]	(10)		(19)
Actuarial loss (gain)	[2]	(4)		7
Plan amendments	[2]	0		(10)
Plan settlement	[1],[2]	0		0
Benefit obligation at end of year	[2]	$ 130		$ 132		$ 142

[1] Represents TECO Energy’s SERP and Restoration settlement charges as a result of the retirement of certain executives. These charges did impact TEC’s financial statements.

[2] Represent amounts for TECO Energy’s Florida-based other postretirement benefit plan.

[3] Represents amounts for TECO Energy’s Florida-based other postretirement benefit plan