Jointly-owned Plant Jointly Owned Plant (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 1985
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman transferred	15.00%		15.00%
Asset Retirement Obligation Increase related to Boardman plant	$ 7,000,000
Interest in Pacific Northwest Intertie			10.714%
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds	$ 1
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman	80.00%	65.00%