Asset Retirement Obligations - SPPC - Asset Retirement Obligation by Type (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities		$ 7,511	$ 3,120
Asset Retirement Obligation		954	954	$ 921
Other Plant in Service [Member]
Asset Retirement Obligations By Type [Line Items]
Asset Retirement Obligation		43	38
Removal Costs [Member]
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities	[1]	2,349	2,242
Sierra Pacific Power Company [Member]
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities		500	290
Asset Retirement Obligation		10	10	$ 10
Sierra Pacific Power Company [Member] | Asbestos [Member]
Asset Retirement Obligations By Type [Line Items]
Asset Retirement Obligation		5	4
Sierra Pacific Power Company [Member] | Evaporative Ponds and Dry Ash Landfills [Member]
Asset Retirement Obligations By Type [Line Items]
Asset Retirement Obligation		2	3
Sierra Pacific Power Company [Member] | Other Plant in Service [Member]
Asset Retirement Obligations By Type [Line Items]
Asset Retirement Obligation		3	3
Sierra Pacific Power Company [Member] | Removal Costs [Member]
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities		$ 211	$ 205

[1] Amounts represent estimated costs, as accrued through depreciation rates and exclusive of ARO liabilities, of removing regulated property, plant and equipment in accordance with accepted regulatory practices. Amounts are deducted from rate base or otherwise accrue a carrying cost.