Commitments and Contingencies, Purchased Power Agreements (Details) - Independent Power Producing Entities - MW	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Purchased Power Agreements [Abstract]
Generating capacity under long term purchased power agreements (in MW)	1,571	1,571
Purchase Power Agreement Expiration (year)	2032

The expiration of purchase power agreements currently under contract (year).

No definition available.

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