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Significant accounting policies (Tables)
 12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]  
Estimated Useful Lives of Depreciable Assets The ranges of estimated useful lives and the weighted average useful lives are summarized below:
Range of useful livesWeighted average useful lives
 2020201920202019
Generation
3 - 60
3 - 60
33
33
Distribution
1 - 100
5 - 100
40
42
Equipment
5 - 50
5 - 44
11
10