Variable-Interest Entities Variable-Interest Entities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	66.67%
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 187		$ 204
Variable Interest Entity (VIE) or Potential VIE, Information Unavailability [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Measure of Activity, Purchases	37		37	37
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 0
Jim Bridger Nos. 1-4 [Member]
Variable Interest Entity [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	67.00%
Jim Bridger Nos. 1-4 [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	66.67%
Jointly Owned Utility Plant, Joint Owner Share	33.33%
Share of coal production purchased by Company	66.67%
Share of coal production purchased by joint venture partner	33.33%
Hermiston [Member]
Variable Interest Entity [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%	[1]
Hermiston [Member] | Variable Interest Entity (VIE) or Potential VIE, Information Unavailability [Member]
Variable Interest Entity [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Percentage of natural gas for jointly owned utility plant procured by Company	100.00%
Percentage of electricity from jointly owned utility plant received by Company	100.00%
Percentage of electricity acquired from jointly owned utility plant by Company through long-term power purchase agreement	50.00%
Jointly Owned Utility Plant, Joint Owner Share	50.00%

[1] As discussed in Note 17, PacifiCorp has contracted to purchase the remaining 50% of the output of the Hermiston generating facility.