Regulatory Matters - SPPC - Other (Details) - Sierra Pacific Power Company [Member] - Public Utilities Commission, Nevada [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) number	Dec. 31, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Impact Fee Payment Term | number	3
Energy Efficiency Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Customer Refund Liability, Current	$ 1	$ 2
Electric Distribution [Member] | General Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	3
Gas Distribution [Member] | General Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 2