Income Taxes - NPC - 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)
Nevada Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	209	201
Deferred Tax Assets, Tax Deferred Expense, Leases	97	100
Employee benefits	15	18
Deferred Tax Assets, Customer Advances	18	14
Other	9	6
Total deferred income tax assets	348	339
Property-related items	(799)	(796)
Regulatory assets	(196)	(206)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(94)	(97)
Other	(8)	(7)
Total deferred income tax liabilities	(1,097)	(1,106)
Net deferred income tax liability	$ (749)	$ (767)