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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