Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Total regulatory assets		$ 4,457	$ 4,285
Regulatory assets		150	130
Regulatory assets		4,307	4,155
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		2,800	2,300
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Total regulatory assets	[1]	1,754	1,577
Abandoned Projects [Member]
Regulatory Assets [Line Items]
Total regulatory assets		159	136
Sierra Pacific Power Company [Member]
Regulatory Assets [Line Items]
Total regulatory assets		435	432
Regulatory assets		25	0
Regulatory assets		410	432
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 305	254
Sierra Pacific Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	[2]	10 years
Total regulatory assets	[2]	$ 128	126
Sierra Pacific Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	[3]	27 years
Total regulatory assets	[3]	$ 85	90
Sierra Pacific Power Company [Member] | Acquisition-related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		30 years
Total regulatory assets		$ 80	83
Sierra Pacific Power Company [Member] | Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		9 years
Total regulatory assets		$ 39	44
Sierra Pacific Power Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		1 year
Total regulatory assets		$ 25	0
Sierra Pacific Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		17 years
Total regulatory assets		$ 22	22
Sierra Pacific Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total regulatory assets		$ 56	$ 67

[1] Amounts primarily represent income tax benefits related to state accelerated tax depreciation and certain property-related basis differences that were previously flowed through to customers and will be included in regulated rates when the temporary differences reverse.

[2] Amounts represent income tax benefits related to accelerated tax depreciation and certain property-related basis differences that were previously flowed through to customers and will be included in regulated rates when the temporary differences reverse

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