Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Total regulatory assets		$ 3,067	$ 2,950
Regulatory assets		171	189
Regulatory assets		2,896	2,761
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 1,300	1,100
Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		2.11940298507463
Total regulatory assets		$ 134	156
Sierra Pacific Power Company [Member]
Regulatory Assets [Line Items]
Total regulatory assets		321	332
Regulatory assets		7	32
Regulatory assets		314	300
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 190	188
Sierra Pacific Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	[1]	8 years
Total regulatory assets	[1]	$ 132	110
Sierra Pacific Power Company [Member] | Acquisition-related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		28 years
Total regulatory assets		$ 74	77
Sierra Pacific Power Company [Member] | Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		7 years
Total regulatory assets		$ 29	34
Sierra Pacific Power Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		1 year
Total regulatory assets		$ 4	23
Sierra Pacific Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		16 years
Total regulatory assets		$ 19	21
Sierra Pacific Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total regulatory assets		$ 63	$ 67

[1] Represents amounts not yet recognized as a component of net periodic benefit cost that are expected to be included in regulated rates when recognized.