Contingencies (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015 claims	Jun. 30, 2013 claims	Dec. 31, 1997	Sep. 30, 2008	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
Loss Contingency, Claims Settled, Number	2
Contracts	119
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	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	2
Loss Contingency, Pending Claims, Number	40	39