Income Taxes - NPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 1,707	$ 909
Employee benefits	45	209
Other	448	707
Total deferred income tax assets	3,543	3,167
Valuation allowances	(126)	(64)
Property-related items	(9,950)	(14,237)
Regulatory assets	(651)	(1,449)
Other	(215)	(334)
Total deferred income tax liabilities	(11,659)	(16,982)
Net deferred income tax liability	(8,242)	(13,879)
Nevada Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	201	83
Deferred Tax Assets, Tax Deferred Expense, Leases	100	170
Employee benefits	18	29
Deferred Tax Assets, Customer Advances	14	23
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal	0	5
Other	6	16
Total deferred income tax assets	339	326
Valuation allowances	0	(5)
Deferred Tax Assets, Net	339	321
Property-related items	(796)	(1,293)
Regulatory assets	(206)	(321)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(97)	(165)
Other	(7)	(16)
Total deferred income tax liabilities	(1,106)	(1,795)
Net deferred income tax liability	$ (767)	$ (1,474)