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, 2022	Dec. 31, 2021	Dec. 31, 2020
Company's contributions to 401(k) plans
Company contributions to defined contribution plans	$ 26	$ 25	$ 22
South Texas Project
STP Defined Benefit Plans
Amount reimbursed to STPNOC towards defined benefit plans	18	17
Expected reimbursement of contribution to retirement plan obligations to STPNOC in 2023	10
Benefit Payments
NRG's expected future benefit payments
2023	83
2024	81
2025	79
2026	77
2027	76
2028-2032	361
STP Defined Benefit Plans
Curtailment gain	(14)	(2)	0
Increase to pension liability	0	0
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP
Funded status — STPNOC benefit plans	(192)	(116)
Net periodic benefit cost/(credit)	18	(27)	(8)
Other changes in plan assets and benefit obligations recognized in other comprehensive income	57	(75)
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)	(50)
Net periodic benefit cost/(credit)	2	17
Other changes in plan assets and benefit obligations recognized in other comprehensive income	(27)	(51)
Other Postretirement Benefits Plan
NRG's expected future benefit payments
2023	7
2024	7
2025	6
2026	6
2027	6
2028-2032	27
Medicare prescription drug reimbursements
2023	0
2024	0
2025	0
2026	0
2027	0
2028-2032	2
STP Defined Benefit Plans
Curtailment gain	0	(1)	0
Increase to pension liability	0	(1)
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP
Funded status — STPNOC benefit plans	(84)	(105)
Net periodic benefit cost/(credit)	(4)	(6)	$ (10)
Other changes in plan assets and benefit obligations recognized in other comprehensive income	(5)	9
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)	(18)
Net periodic benefit cost/(credit)	(4)	(4)
Other changes in plan assets and benefit obligations recognized in other comprehensive income	$ 1	$ 4
South Texas Project
STP Defined Benefit Plans
Ownership interest in STP (as a percent)	44.00%
Percentage of contribution to the retirement plan obligation reimbursed	44.00%

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