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Summary of Significant Accounting Policies - Capacity Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Revenue from External Customer [Line Items] |  |  |  |  |  |  |
Estimated revenue for cleared auction MWs, capacity auctions | $ 1,928 | $ 3,751 |  |  |  |  |
Capacity revenue |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |
Estimated revenue for cleared auction MWs, capacity auctions | $ 313 | $ 601 |  |  |  |  |
Scenario, Forecast | Capacity revenue |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |
Estimated revenue for cleared auction MWs, capacity auctions |  |  | $ 168 | $ 388 | $ 410 | $ 519 | $ 578

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