Contingencies (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013 claims	Dec. 31, 2012	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2005	Dec. 31, 1997	Sep. 30, 2008	Sep. 30, 2000	Dec. 31, 1993
Loss Contingencies [Line Items]
investment in Trojan										87.00%
Regulatory asset related to Trojan									$ 5,000,000
Refund to customers for Trojan Investment including interest								33,100,000
Class action damages sought		260,000,000
Site Contingency, Names of Other Potentially Responsible Parties		100			6	14	69
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
Claims moved to dismiss		36
Loss Contingency, Pending Claims, Number		39
Low 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
Repayments of Pollution Control Bond				5,800,000
Potential Income Tax Liability related to State Tax Court Ruling		7,000,000
Damages sought in USDOE claim			112,000,000
Loss Contingency, Damages Awarded, Value	70,000,000
Gain Contingency, Unrecorded Amount		$ 44,000,000