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Asset Impairments (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 05, 2018 | Sep. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Feb. 20, 2019
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses, other assets |  |  |  |  |  |  | $ 14,000,000 | $ 12,000,000 |  |
Impairment losses |  |  |  |  |  |  | 75,000,000 | 5,000,000 | $ 99,000,000 |
Equity method investments |  |  |  |  |  |  | 346,000,000 | 388,000,000 |  |
Impairment losses on investments |  |  |  |  |  |  | 18,000,000 | $ 108,000,000 | 15,000,000 |
Held-for-sale | NRG Solar Guam, LLC |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses |  |  |  |  | $ 12,000,000 |  |  |  |  |
Cash consideration |  |  |  |  |  |  |  |  |  | $ 8,000,000
Cottonwood | West/Other |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  |  |  |  |  |  | $ 32,000,000 |  |  |
Home Solar | West/Other |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  | $ 29,000,000 |  |  |  |  |  |  |  |
Petra Nova Parish Holdings |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  |  |  | $ 101,000,000 |  |  |  |  |  |
Letter of credit |  |  |  | 12,000,000 |  |  |  |  |  |
Contribution in cash |  |  |  | 95,000,000 |  |  |  |  |  |
Guarantee (up to) |  |  |  | $ 124,000,000 |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  | 50.00% |  |  |
Equity method investments |  |  |  |  |  |  | $ (13,000,000) |  |  |
Petra Nova Parish Holdings | Texas |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments |  |  | $ 18,000,000 |  |  |  |  |  |  |
Keystone |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments | $ 14,000,000 |  |  |  |  |  |  |  |  |
Ownership percentage | 3.70% |  |  |  |  |  |  |  |  |
Conemaugh |  |  |  |  |  |  |  |  |  |
Asset Impairments |  |  |  |  |  |  |  |  |  |
Impairment losses on equity method investments | $ 14,000,000 |  |  |  |  |  |  |  |  |
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 |

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