Commitments and Contingencies, Purchased Power Agreements (Details) - Independent Power Producing Entities - MW	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	1,197	1,197
Purchase Power Agreement Expiration (year)	2041	2041

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

No definition available.

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Period Type:	duration