Variable-Interest Entities - PacifiCorp (Details) - PacifiCorp [Member] - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity (VIE) or Potential VIE, Information Unavailability [Member]
Schedule of Equity Method Investments [Line Items]
Variable Interest Entity, Measure of Activity, Purchases		$ 39,000,000	$ 38,000,000	$ 38,000,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 0
Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		66.67%
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net		$ 190,000,000	$ 192,000,000
Hermiston [Member]
Schedule of Equity Method Investments [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	[1]	50.00%
Hermiston [Member] | Variable Interest Entity (VIE) or Potential VIE, Information Unavailability [Member]
Schedule of Equity Method Investments [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%
Jim Bridger Unit Nos 1 thru 4 [Member]
Schedule of Equity Method Investments [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share		67.00%
Jim Bridger Unit Nos 1 thru 4 [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [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%

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