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Benefit Plans and Other Postretirement Benefits - Expected Future Benefit Payments for the Next Five Years and Other (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Company's contributions to 401(k) plans |  |  |
Company contributions to defined contribution plans | $ 61 | $ 37 | $ 35
South Texas Project |  |  |
STP Defined Benefit Plans |  |  |
Amount reimbursed to STPNOC towards defined benefit plans | $ 3 | 18 |
STP |  |  |
STP Defined Benefit Plans |  |  |
Percentage of contribution to the retirement plan obligation reimbursed | 44.00% |  |
Benefit Payments |  |  |
NRG's expected future benefit payments |  |  |
2024 | $ 82 |  |
2025 | 81 |  |
2026 | 79 |  |
2027 | 78 |  |
2028 | 76 |  |
2029-2033 | 360 |  |
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP |  |  |
Funded status — STPNOC benefit plans | (172) | (192) |
Net periodic benefit cost/(credit) | 21 | 18 | (27)
Other changes in plan assets and benefit obligations recognized in other comprehensive income | (38) | 57 |
Benefit Payments | South Texas Project |  |  |
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP |  |  |
Funded status — STPNOC benefit plans |  | (7) |
Net periodic benefit cost/(credit) |  | 2 |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  | (27) |
Other Postretirement Benefits Plan |  |  |
NRG's expected future benefit payments |  |  |
2024 | 5 |  |
2025 | 5 |  |
2026 | 5 |  |
2027 | 5 |  |
2028 | 5 |  |
2029-2033 | 27 |  |
Medicare prescription drug reimbursements |  |  |
2024 | 0 |  |
2025 | 0 |  |
2026 | 0 |  |
2027 | 0 |  |
2028 | 0 |  |
2029-2033 | 2 |  |
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP |  |  |
Funded status — STPNOC benefit plans | (75) | (84) |
Net periodic benefit cost/(credit) | (3) | (4) | $ (6)
Other changes in plan assets and benefit obligations recognized in other comprehensive income | $ 1 | (5) |
Other Postretirement Benefits Plan | South Texas Project |  |  |
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP |  |  |
Funded status — STPNOC benefit plans |  | (13) |
Net periodic benefit cost/(credit) |  | (4) |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  | $ 1 |

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