Transactions With Affiliates Transactions with Affiliates (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
EWO Marketing, LLC [Member] \| RS Cogen [Member]
Related Party Transaction [Line Items]
Capacity Charge and Gas Transportation Expense	$ 24.6	$ 24.7	$ 24.5

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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