Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 1,420	$ 1,610
Other	777	590
Total deferred income tax assets	3,178	3,081
Property-related items	(10,816)	(10,439)
Regulatory assets	(785)	(631)
Other	(327)	(384)
Total deferred income tax liabilities	(14,749)	(12,591)
Net deferred income tax liability	(11,775)	(9,653)
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	67	70
Employee benefits	2	6
Deferred Tax Assets, Tax Deferred Expense, Leases	30	13
Deferred Tax Assets, Customer Advances	10	9
Other	8	6
Total deferred income tax assets	117	104
Property-related items	(380)	(370)
Regulatory assets	(74)	(62)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(30)	(13)
Other	(7)	(6)
Total deferred income tax liabilities	(491)	(451)
Net deferred income tax liability	$ (374)	$ (347)