Contingencies (Details)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013 claims	Jun. 30, 2015 USD ($) claims	Dec. 31, 1997	Dec. 31, 2014 USD ($)	Sep. 30, 2008 USD ($)	Dec. 31, 1993
Loss Contingencies [Line Items]
Investment in Trojan						87.00%
Refund to customers for Trojan Investment including interest					$ 33,000,000
Class action damages sought		$ 260,000,000
Site Contingency, Names of Other Potentially Responsible Parties		100	69
Lower estimate of range of cost of Portland Harbor cleanup in total		$ 169,000,000
Upper estimated range of total cost of Portland Harbor cleanup		1,800,000,000
Remediation cost estimate lower range		3,000,000
Remediation cost estimate upper range		8,000,000
Loss Contingency, Estimate of Possible Loss		3,000,000
Regulatory asset for recovery of loss contingencies		2,000,000		$ 3,000,000
Civil Penalty Claim - Per day per violation through January 12, 2009		32,500
Civil Penalty Claim - Per day per violation after January 12, 2009		$ 37,500
Loss Contingency, Actions Taken by Defendant	36
projects added to plaintiff's suit | claims		2
Loss Contingency, Pending Claims, Number | claims	39	40