Income Taxes - NPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 909	$ 834
Employee benefits	209	190
Other	707	815
Total deferred income tax assets	3,167	3,104
Valuation allowances	(64)	(35)
Total deferred income tax assets, net	3,103	3,069
Property-related items	(14,237)	(13,157)
Regulatory assets	(1,449)	(1,446)
Other	(334)	(299)
Total deferred income tax liabilities	(16,982)	(15,754)
Deferred Tax Liabilities, Net	13,879	12,685
Nevada Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Tax Deferred Expense, Leases	170	174
Regulatory liabilities	83	47
Employee benefits	29	30
Deferred Tax Assets, Customer Advances	23	22
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal	5	15
Other	16	17
Total deferred income tax assets	326	305
Valuation allowances	(5)	(5)
Total deferred income tax assets, net	321	300
Property-related items	(1,293)	(1,242)
Regulatory assets	(321)	(275)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(165)	(169)
Other	(16)	(19)
Total deferred income tax liabilities	(1,795)	(1,705)
Deferred Tax Liabilities, Net	$ 1,474	$ 1,405