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, 2021	Dec. 31, 2020	Dec. 31, 2019
STP Defined Benefit Plans
Curtailment gain			$ 8
Increase to pension liability			32
Company's contributions to 401(k) plans
Company contributions to defined contribution plans	$ 25	$ 22	22
South Texas Project
STP Defined Benefit Plans
Amount reimbursed to STPNOC towards defined benefit plans	17	8
Expected reimbursement of contribution to retirement plan obligations to STPNOC in 2014	13
Pension Benefit Payments
NRG's expected future benefit payments
2022	96
2023	94
2024	91
2025	87
2026	86
2027-2031	396
STP Defined Benefit Plans
Curtailment gain	(2)	0	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	(116)	(217)
Net periodic benefit credit	(27)	(8)	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income	(75)	(11)
Pension 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	(50)	(99)
Net periodic benefit credit	17	7
Other changes in plan assets and benefit obligations recognized in other comprehensive income	(51)	22
Other Postretirement Benefits Plan
NRG's expected future benefit payments
2022	7
2023	7
2024	7
2025	6
2026	6
2027-2031	26
Medicare prescription drug reimbursements
2022	0
2023	0
2024	0
2025	0
2026	0
2027-2031	2
STP Defined Benefit Plans
Curtailment gain	(1)	0	0
Increase to pension liability	(1)	0
Recognized amount in statement of financial position, statement of operations and accumulated OCI related to STP
Funded status — STPNOC benefit plans	(105)	(90)
Net periodic benefit credit	(6)	(10)	$ (9)
Other changes in plan assets and benefit obligations recognized in other comprehensive income	9	13
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	(18)	(20)
Net periodic benefit credit	(4)	(4)
Other changes in plan assets and benefit obligations recognized in other comprehensive income	$ 4	$ 5
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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