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Summary of Significant Accounting Policies Estimated average service lives (Details) | 12 Months Ended
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Dec. 31, 2017
Generation, excluding thermal: |
Hydro | 95
Wind | 30
Transmission | 57
Distribution | 45
General | 12

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- Definition estimated average service life - hydro production plant + References No definition available. + Details
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- Definition estimated average service life - wind production plant + References No definition available. + Details
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- Definition estimated average service lives - distribution plant + References No definition available. + Details
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- Definition estimated average service lives - general plant + References No definition available. + Details
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- Definition estimated average service lives - transmission plant + References No definition available. + Details
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- Definition Production plant, excluding thermal: [Abstract] + References No definition available. + Details
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