Income Taxes - NPC - 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)
Nevada Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	206	211
Deferred Tax Assets, Tax Deferred Expense, Leases	79	99
Employee benefits	8	14
Deferred Tax Assets, Customer Advances	19	19
Other	15	9
Total deferred income tax assets	327	352
Property-related items	(800)	(797)
Regulatory assets	(176)	(166)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(76)	(95)
Other	(13)	(8)
Total deferred income tax liabilities	(1,065)	(1,066)
Net deferred income tax liability	$ (738)	$ (714)