Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 1,674	$ 1,707
Employee benefits	68	45
Other	459	450
Total deferred income tax assets	3,029	3,543
Property-related items	(10,185)	(9,950)
Regulatory assets	(656)	(651)
Other	(222)	(215)
Total deferred income tax liabilities	(11,939)	(11,659)
Net deferred income tax liability	(9,047)	(8,242)
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	70	67
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal	0	10
Employee benefits	10	10
Deferred Tax Assets, Tax Deferred Expense, Leases	8	7
Deferred Tax Assets, Customer Advances	8	7
Other	6	6
Total deferred income tax assets	102	107
Property-related items	(346)	(349)
Regulatory assets	(73)	(74)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(8)	(7)
Other	(6)	(7)
Total deferred income tax liabilities	(433)	(437)
Net deferred income tax liability	$ (331)	$ (330)