Regulatory - Additional Information (Detail)						9 Months Ended	12 Months Ended
	Jan. 31, 2027 USD ($)	Jan. 31, 2026 USD ($)	Jan. 31, 2025 USD ($)	Oct. 09, 2024 USD ($) Customer	Sep. 26, 2024 USD ($) Customer	Sep. 30, 2024 USD ($)	May 31, 2025 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Public Utilities General Disclosures [Line Items]
Accumulated depreciation						$ 3,604,000,000			$ 3,443,000,000
Regulatory asset for storm restoration costs						$ 945,000,000			$ 988,000,000
Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Adjustments to fuel and capacity charges reduction over period							$ 138,000,000
Storm Restoration Cost Recovery [Member]
Public Utilities General Disclosures [Line Items]
Minimum cost recovery period						12 months
Reserve liability for storm restoration cost								$ 5,000,000
Regulatory asset for storm restoration costs						$ 35,000,000
Tampa Electric Base Rates, on April 02, 2024 [Member] | Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Effect of base rate adjustment on revenue	$ 72,000,000	$ 100,000,000	$ 297,000,000
Tampa Electric Base Rates on August 22, 2024 [Member] | Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Effect of base rate adjustment on revenue	$ 65,000,000	$ 92,000,000	$ 288,000,000
Hurricane Helene [Member]
Public Utilities General Disclosures [Line Items]
Number of customers impacted by storm | Customer					100,000
Hurricane Helene [Member] | Minimum [Member]
Public Utilities General Disclosures [Line Items]
Storm restoration costs charged to reserve					$ 45,000,000
Hurricane Helene [Member] | Maximum [Member]
Public Utilities General Disclosures [Line Items]
Storm restoration costs charged to reserve					$ 55,000,000
Hurricane Milton [Member]
Public Utilities General Disclosures [Line Items]
Number of customers impacted by storm | Customer				600,000
Number of years worst weather event impact on area				100 years
Hurricane Milton [Member] | Minimum [Member] | Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Storm restoration costs charged to reserve				$ 320,000,000
Hurricane Milton [Member] | Maximum [Member] | Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Storm restoration costs charged to reserve				$ 370,000,000