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Benefit Plans and Other Postretirement Benefits - Amounts Recognized in the Balance Sheets and OCI (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 14, 2018 | Jun. 14, 2017
Pension Benefits |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | $ 0 | $ 0 |  |  |
Non-current liabilities | 241 | 225 |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Net loss/(gain) | 90 | 53 |  |  |
Prior service cost/(credit) | 3 | 3 |  |  |
Total accumulated OCI | 93 | 56 |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Net actuarial loss/(gain) | 47 | (37) |  |  |
Amortization of net actuarial (gain)/loss | 0 | (4) | $ (2) |  |
Curtailment | (27) | 0 |  |  |
Prior service credit | 17 | 0 |  |  |
Amortization of prior service cost | 0 | 0 |  |  |
Total recognized in other comprehensive loss | 37 | (41) |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | 49 | (11) |  |  |
Estimated unrecognized loss for NRG's pension plan that will be amortized from accumulated OCI to net periodic cost over the next fiscal year (less than) | 4 |  |  |  |
Significant components of NRG's domestic pension plan |  |  |  |  |
Projected benefit obligation | 1,222 | 1,329 | 1,241 |  |
Accumulated benefit obligation | 1,188 | 1,255 |  |  |
Fair value of plan assets | 981 | 1,104 | 953 |  |
Other Postretirement Benefit |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | 7 | 7 |  |  |
Non-current liabilities | 76 | 121 |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Net loss/(gain) | (9) | (4) |  |  |
Prior service cost/(credit) | (53) | (37) |  |  |
Total accumulated OCI | (62) | (41) |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Net actuarial loss/(gain) | (5) | 6 |  |  |
Amortization of net actuarial (gain)/loss | 0 | 1 | 0 |  |
Curtailment | 2 | 0 |  |  |
Prior service credit | (28) | (1) |  |  |
Amortization of prior service cost | 10 | 9 |  |  |
Total recognized in other comprehensive loss | (21) | 15 |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | (36) | 13 |  |  |
Expected unrecognized gain that will be amortized from accumulated OCI to net periodic cost over the next fiscal year | 1 |  |  |  |
Expected amortization of unrecognized prior service credit over the next fiscal Year |  | 13 |  |  |
Significant components of NRG's domestic pension plan |  |  |  |  |
Projected benefit obligation | 83 | 128 | 128 |  |
Fair value of plan assets | 0 | 0 | $ 0 |  |
GenOn |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Pension benefit obligations | 92 |  |  |  |
Liability retained other post-employment and retiree health and welfare benefits | 25 |  |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Net loss/(gain) | (28) |  |  |  |
GenOn | Pension Benefits |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | 0 | 0 |  |  |
Non-current liabilities | 0 | 0 |  |  |
Liability retained other post-employment and retiree health and welfare benefits | 0 | 0 |  |  |
Significant components of NRG's domestic pension plan |  |  |  |  |
Projected benefit obligation | 0 | 0 |  |  |
GenOn | Other Postretirement Benefit |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | 0 | 3 |  |  |
Non-current liabilities | 0 | 10 |  |  |
Liability retained other post-employment and retiree health and welfare benefits | 0 | 25 |  |  | $ 25
Significant components of NRG's domestic pension plan |  |  |  |  |
Projected benefit obligation | 0 | 38 |  | $ 23 |
NRG | Pension Benefits |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | 0 | 0 |  |  |
Non-current liabilities | 241 | 225 |  |  |
NRG | Other Postretirement Benefit |  |  |  |  |
Amounts recognized in balance sheet |  |  |  |  |
Current liabilities | 7 | 4 |  |  |
Non-current liabilities | 76 | 111 |  |  |
Discontinued Operations | Pension Benefits |  |  |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Total accumulated OCI | 0 | (22) |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Total recognized in other comprehensive loss | 0 | 15 |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | 0 | 0 |  |  |
Discontinued Operations | Other Postretirement Benefit |  |  |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Total accumulated OCI | 0 | 10 |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Total recognized in other comprehensive loss | 0 | 2 |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | 0 | 1 |  |  |
Continuing Operations | Pension Benefits |  |  |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Total accumulated OCI | 93 | 34 |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Total recognized in other comprehensive loss | 37 | (26) |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | 12 | 15 |  |  |
Continuing Operations | Other Postretirement Benefit |  |  |  |  |
Amounts recognized in accumulated OCI |  |  |  |  |
Total accumulated OCI | (62) | (31) |  |  |
Other changes in plan assets and benefit obligations recognized in other comprehensive income |  |  |  |  |
Total recognized in other comprehensive loss | (21) | 17 |  |  |
Net recognized in net periodic pension cost/(credit) and OCI | $ (15) | $ (5) |  |  |

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