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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract] |
Estimated average service lives [Table Text Block] | Depreciation is provided on PGE’s other classes of plant in service over their estimated average service lives, which are as follows (in years):
Generation, excluding thermal: |
Hydro | 95 |
Wind | 30 |
Transmission | 57 |
Distribution | 45 |
General | 12 |

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