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Debt and Capital Leases - Alta Wind Lease Financings Arrangements (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Debt Instrument |  |
Long-term debt | $ 16,633 | $ 16,704
Total | Low |  |
Debt Instrument |  |
Interest rate, stated percentage | 5.696% |
Total | Maximum |  |
Debt Instrument |  |
Interest rate, stated percentage | 7.015% |
Alta Wind Holdings | Alta Wind I | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 231 |
Interest rate, stated percentage | 7.015% |
Alta Wind Holdings | Alta Wind I | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 16 |
Alta Wind Holdings | Alta Wind I | Letter of Credit | Low |  |
Debt Instrument |  |
Interest rate, stated percentage | 3.00% |
Alta Wind Holdings | Alta Wind I | Letter of Credit | Maximum |  |
Debt Instrument |  |
Interest rate, stated percentage | 3.25% |
Alta Wind Holdings | Alta Wind II | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 183 |
Interest rate, stated percentage | 5.696% |
Alta Wind Holdings | Alta Wind II | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 27 |
Interest rate, stated percentage | 1.25% |
Alta Wind Holdings | Alta Wind III | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 191 |
Interest rate, stated percentage | 6.067% |
Alta Wind Holdings | Alta Wind III | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 27 |
Interest rate, stated percentage | 1.75% |
Alta Wind Holdings | Alta Wind IV | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 123 |
Interest rate, stated percentage | 5.938% |
Alta Wind Holdings | Alta Wind IV | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 19 |
Interest rate, stated percentage | 1.75% |
Alta Wind Holdings | Alta Wind V | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 198 |
Interest rate, stated percentage | 6.071% |
Alta Wind Holdings | Alta Wind V | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 30 |
Interest rate, stated percentage | 1.75% |
Alta Wind Holdings | Total | Leasing Arrangement |  |
Debt Instrument |  |
Long-term debt | $ 926 |
Alta Wind Holdings | Total | Letter of Credit |  |
Debt Instrument |  |
Long-term debt | $ 119 |

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