Employee Postretirement Benefits - Schedule of Change in Benefit Obligation (Detail) - TECO Energy [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year		$ 850	$ 919
Service cost		18	19	$ 20
Interest cost		23	21	26
Plan participants’ contributions		0	0
Benefits paid		(79)	(77)
Actuarial gain		(142)	(32)
Plan settlement	[1]	(4)	0
Benefit obligation at end of year		666	850	919
Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	[2]	200	212
Service cost	[2]	2	2	2
Interest cost	[2]	5	5	6
Plan participants’ contributions	[2]	4	4
Benefits paid	[2]	(19)	(17)
Actuarial gain	[2]	(50)	(6)
Plan settlement	[1],[2]	0	0
Benefit obligation at end of year	[2]	$ 142	$ 200	$ 212

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