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Asset Impairments (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 05, 2018 | Sep. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Jun. 30, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Feb. 20, 2019 | Dec. 31, 2014
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses, other assets |  |  |  |  |  |  | $ 12,000,000 |  |  |  |
Impairment losses |  |  |  |  |  |  | 5,000,000 | $ 99,000,000 | $ 1,534,000,000 |  |
Equity method investments |  |  | $ 412,000,000 |  |  |  | 388,000,000 | 412,000,000 |  |  |
Impairment losses on investments |  |  |  |  |  |  | $ 108,000,000 | 15,000,000 | 79,000,000 |  |
Emission Allowances |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses |  |  |  |  |  |  |  |  | 20,000,000 |  |
Renewables |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses |  |  |  |  |  |  |  |  | 29,000,000 |  |
Construction in Progress |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses |  |  |  |  |  | $ 41,000,000 |  |  |  |  |
Construction in progress |  |  |  |  |  | $ 0 |  |  |  |  |
Held-for-sale | NRG Solar Guam, LLC |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses |  |  | $ 12,000,000 |  |  |  |  |  |  |  |
Cash consideration |  |  |  |  |  |  |  |  |  | $ 8,000,000 |
Petra Nova |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Contribution in cash |  | $ 95,000,000 |  |  |  |  |  |  |  |  |
Letter of credit |  | 12,000,000 |  |  |  |  |  |  |  |  |
Guarantee (up to) |  | 124,000,000 |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  | $ 101,000,000 |  |  |  |  |  |  |  |  |
Keystone |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments | $ 14,000,000 |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  |  |  | 3.70%
Impairment losses on investments |  |  |  |  |  |  |  |  | 35,000,000 |  |
Conemaugh |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments | $ 14,000,000 |  |  |  |  |  |  |  |  |  |
Impairment losses on investments |  |  |  |  |  |  |  |  | 35,000,000 |  |
Dunkirk |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  |  |  | $ 46,000,000 |  |  |  |  |  |  |
Equity method investments |  |  |  | $ 0 |  |  |  |  |  |  |
Other Investments |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  |  |  |  |  |  |  | 15,000,000 |  |  |
Impairment losses on investments |  |  |  |  |  |  |  | $ 13,000,000 | 10,000,000 |  |
South Texas Project |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on investments |  |  |  |  |  |  |  |  | 1,248,000,000 |  |
Indian River |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Impairment losses on investments |  |  |  |  |  |  |  |  | $ 36,000,000 |  |
Petra Nova Parish Holdings |  |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  | 50.00% |  |  |  | 50.00% |  |
Impairment losses on investments |  |  |  |  | $ 69,000,000 |  |  |  |  |  |

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