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, 2023		Dec. 31, 2022		Dec. 31, 2021
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost		$ 1		$ 8		$ 10
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost		5		9		11
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		15		18		19
Interest cost		35		23		21
Expected return on plan assets		(54)		(51)		(52)
Amortization of:
Actuarial loss		5		17		24
Prior service cost		$ 0		$ 0		$ 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]		Nonoperating Income (Expense)		Nonoperating Income (Expense)		Nonoperating Income (Expense)
Settlement loss	[1]	$ 2		$ 2		$ 0
Net periodic benefit cost		3		9		12
Net loss (gain) arising during the year (includes curtailment gain)		2		123		(56)
Prior service cost		0		0		0
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		(7)		(19)		(23)
Total recognized in OCI and regulatory assets		(5)		104		(79)
Total recognized in net periodic benefit cost, OCI and regulatory assets		(2)		113		(67)
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[3]	1	[2]	2	[2]	2
Interest cost	[3]	7	[2]	5	[2]	5
Expected return on plan assets	[3]	0		0		0
Amortization of:
Actuarial loss	[3]	0		3		4
Prior service cost	[3]	$ (2)		$ (2)		$ (2)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]		Nonoperating Income (Expense)		Nonoperating Income (Expense)		Nonoperating Income (Expense)
Settlement loss	[1],[3]	$ 0		$ 0		$ 0
Net periodic benefit cost	[3]	6		8		9
Net loss (gain) arising during the year (includes curtailment gain)	[3]	7		(50)		(5)
Prior service cost	[3]	(11)		0		0
Amounts recognized as component of net periodic benefit cost:
Amortization or curtailment recognition of prior service credit	[3]	3		2		2
Amortization or settlement of actuarial loss	[3]	0		(3)		(4)
Total recognized in OCI and regulatory assets	[3]	(1)		(51)		(7)
Total recognized in net periodic benefit cost, OCI and regulatory assets	[3]	$ 5		$ (43)		$ 2

[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