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Employee Postretirement Benefits - Schedule of Benefit Payments (Detail) - TECO Energy [Member]
$ in Millions
Dec. 31, 2019
USD ($)
Pension Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected Benefit Payments - 2020 $ 55
Expected Benefit Payments - 2021 61
Expected Benefit Payments - 2022 61
Expected Benefit Payments - 2023 61
Expected Benefit Payments - 2024 63
Expected Benefit Payments - 2025 - 2029 342
Other Postretirement Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected Benefit Payments - 2020 12
Expected Benefit Payments - 2021 12
Expected Benefit Payments - 2022 11
Expected Benefit Payments - 2023 11
Expected Benefit Payments - 2024 11
Expected Benefit Payments - 2025 - 2029 $ 53