Summary of Significant Accounting Policies Summary of Significant Accounting Policies - SPPC - New Accounting Pronouncements (Details) (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 02, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 1,085
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prior Period Reclassification Adjustment			$ (8)	$ 4
Accounting Standards Update 2017-07 [Member] | Sierra Pacific Power Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prior Period Reclassification Adjustment			$ 1	$ (1)
Scenario, Forecast [Member] | Operating Lease [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 550
Scenario, Forecast [Member] | Operating Lease [Member] | Accounting Standards Update 2016-02 [Member] | Sierra Pacific Power Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 20