Employee Postretirement Benefits - Schedule of Change in Benefit Obligation (Detail) - TECO Energy [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Pension Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year		$ 919		$ 843
Service cost		19		20		$ 20
Interest cost		21		26		31
Plan participants’ contributions		0		0
Benefits paid		(77)		(54)
Actuarial (gain) loss		(32)		84
Benefit obligation at end of year		850		919		843
Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	[1]	212		180
Service cost		2	[1]	2	[1]	1
Interest cost		5	[1]	6	[1]	7
Plan participants’ contributions	[1]	4		4
Benefits paid	[1]	(17)		(17)
Actuarial (gain) loss	[1]	(6)		37
Benefit obligation at end of year	[1]	$ 200		$ 212		$ 180

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