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Commitments and Contingencies (Schedule of Long-Term Purchase Agreements) (Detail)
$ in Millions
Dec. 31, 2020
USD ($)
[1]
Commitments And Contingencies Disclosure [Abstract]  
Purchased electric capacity, 2021 $ 83
Purchased electric capacity, 2022 82
Purchased electric capacity, 2023 82
Purchased electric capacity, 2024 81
Purchased electric capacity, 2025 82
Purchased electric capacity, Thereafter 915
Purchased electric capacity, Total $ 1,325
[1] (1)   Includes affiliated amounts with certain solar facilities of $246 million