Leases - Summary of Lease Assets and Liabilities (Detail) - Tampa Electric [Member] - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Schedule Of Assets And Liabilities Lessee [Line Items]
Right-of-use asset	$ 19	$ 21
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Deferred Costs and Other Assets	Deferred Costs and Other Assets
Current	$ 2	$ 2
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Long-term	$ 18	$ 20
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Deferred Credits and Other Liabilities, Noncurrent	Deferred Credits and Other Liabilities, Noncurrent
Total lease liabilities	$ 20	$ 22