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, 2024		Dec. 31, 2023		Dec. 31, 2022
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost		$ 0		$ 1		$ 8
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost		4		5		9
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		17		15		18
Interest cost		35		35		23
Expected return on plan assets		(55)		(54)		(51)
Amortization of:
Actuarial loss		7		5		17
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]	$ 0		$ 2		$ 2
Net periodic benefit cost		4		3		9
Net loss (gain) arising during the year (includes curtailment gain)		15		2		123
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)		(7)		(19)
Total recognized in OCI and regulatory assets		8		(5)		104
Total recognized in net periodic benefit cost, OCI and regulatory assets		12		(2)		113
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[3]	1	[2]	1	[2]	2
Interest cost	[3]	7	[2]	7	[2]	5
Expected return on plan assets	[3]	0		0		0
Amortization of:
Actuarial loss	[3]	0		0		3
Prior service cost	[3]	$ 3		$ 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]	5		6		8
Net loss (gain) arising during the year (includes curtailment gain)		(4)	[3]	7	[2]	(50)	[3]
Prior service cost	[3]	0		(11)		0
Amounts recognized as component of net periodic benefit cost:
Amortization or curtailment recognition of prior service credit		3	[3]	3	[2]	2	[3]
Amortization or settlement of actuarial loss		0	[3]	0	[2]	(3)	[3]
Total recognized in OCI and regulatory assets		(1)	[3]	(1)	[2]	(51)	[3]
Total recognized in net periodic benefit cost, OCI and regulatory assets		$ 4	[3]	$ 5	[2]	$ (43)	[3]

[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