Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 1,610	$ 1,674
Other	590	527
Total deferred income tax assets	3,081	3,029
Property-related items	(10,439)	(10,185)
Regulatory assets	(631)	(656)
Other	(384)	(222)
Total deferred income tax liabilities	(12,591)	(11,939)
Net deferred income tax liability	(9,653)	(9,047)
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	70	70
Employee benefits	6	10
Deferred Tax Assets, Tax Deferred Expense, Leases	13	8
Deferred Tax Assets, Customer Advances	9	8
Other	6	6
Total deferred income tax assets	104	102
Property-related items	(370)	(346)
Regulatory assets	(62)	(73)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(13)	(8)
Other	(6)	(6)
Total deferred income tax liabilities	(451)	(433)
Net deferred income tax liability	$ (347)	$ (331)