Employee Postretirement Benefits - Schedule of Amounts Recognized in Net Periodic Benefit Cost, OCI, and Regulatory Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 10		$ 12		$ 12
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	11		7		7
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19		20		20
Interest cost	21		26		31
Expected return on plan assets	(52)		(50)		(51)
Amortization of:
Actuarial loss	24		20		16
Prior service (benefit) cost	0		0		0
Settlement loss	0		0		1
Net periodic benefit cost	12		16		17
Net loss (gain) arising during the year (includes curtailment gain)	(56)		(8)		(17)
Amounts recognized as component of net periodic benefit cost:
Amortization or curtailment recognition of prior service credit	0		0		0
Amortization or settlement of actuarial loss	(23)		(20)		(17)
Total recognized in OCI and regulatory assets	(79)		(28)		(34)
Total recognized in net periodic benefit cost, OCI and regulatory assets	(67)		(12)		(17)
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	[1]	2	[1]	1
Interest cost	5	[1]	6	[1]	7
Expected return on plan assets	0		0		0
Amortization of:
Actuarial loss	4		1		1
Prior service (benefit) cost	(2)		(3)		(2)
Settlement loss	0		0		0
Net periodic benefit cost	9		6		7
Net loss (gain) arising during the year (includes curtailment gain)	(5)		38		9
Amounts recognized as component of net periodic benefit cost:
Amortization or curtailment recognition of prior service credit	2		2		2
Amortization or settlement of actuarial loss	(4)		(1)		(1)
Total recognized in OCI and regulatory assets	(7)		39		10
Total recognized in net periodic benefit cost, OCI and regulatory assets	$ 2		$ 45		$ 17

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