Variable-Interest Entities - PacifiCorp (Details) - PacifiCorp [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	$ 137	$ 165
Hermiston [Member]
Schedule of Equity Method Investments [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership 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%