v3.25.2
Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension Benefits [Member]        
Amortization of:        
Net periodic benefit cost $ 1 $ 0 $ 2 $ 0
Other Postretirement Benefits [Member]        
Amortization of:        
Net periodic benefit cost 2 1 3 2
TECO Energy [Member] | Pension Benefits [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost 5 5 9 9
Interest cost 9 8 18 17
Expected return on assets (14) (13) (27) (27)
Amortization of:        
Amortization of actuarial loss (gain) 2 1 4 3
Net periodic benefit cost 2 1 4 2
TECO Energy [Member] | Other Postretirement Benefits [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost 0 0 0 0
Interest cost 1 1 3 3
Expected return on assets 0 0 0 0
Amortization of:        
Amortization of actuarial loss (gain) 0 0 0 (1)
Net periodic benefit cost $ 1 $ 1 $ 3 $ 2