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Benefit Plans and Other Postretirement Benefits - Narrative (Details) $ in Millions | Dec. 31, 2019 USD ($) numberOfBenefitPlans | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
--- | --- | --- | ---
Benefit Plans and Other Postretirement Benefits |  |  |
Number of qualified pension plans | numberOfBenefitPlans | 2 |  |
Pension Benefits |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Expects to contribute to the pension plans | $ 56 |  |
GenOn |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Pension liability retained |  |  | $ 92
Liability retained other post-employment and retiree health and welfare benefits |  | $ 23 |
GenOn | Restructuring Support Agreement |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Amount of pension liability future contributions |  |  | $ 13
Expects to contribute to the pension plans | $ 21 |  |

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