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Regulatory Matters - NPC - Other (Details)
1 Months Ended 9 Months Ended 12 Months Ended
Oct. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
MW
Sep. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
number
Dec. 31, 2017
USD ($)
Dec. 31, 2016
Mar. 31, 2018
USD ($)
Public Utilities, General Disclosures [Line Items]              
Federal statutory income tax rate       21.00% 35.00% 35.00%  
Regulatory assets       $ 2,896,000,000 $ 2,761,000,000    
Tax Cuts and Jobs Act of 2017 [Member]              
Public Utilities, General Disclosures [Line Items]              
Federal statutory income tax rate       21.00%      
Nevada Power Company [Member]              
Public Utilities, General Disclosures [Line Items]              
Customer Refundable Fees, Refund Payments       $ 1,000,000      
Federal statutory income tax rate       21.00% 35.00% 35.00%  
Regulatory assets       $ 878,000,000 $ 941,000,000    
Nevada Power Company [Member] | 257 Megawatts of Coal Energy [Member]              
Public Utilities, General Disclosures [Line Items]              
Coal-Fired Power Plant Capacity | MW   257          
Regulatory assets             $ 151,000,000
Nevada Power Company [Member] | Tax Cuts and Jobs Act of 2017 [Member]              
Public Utilities, General Disclosures [Line Items]              
Federal statutory income tax rate       21.00%      
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Wynn Las Vegas LLC [Member]              
Public Utilities, General Disclosures [Line Items]              
Impact Fee Credit     $ 3,000,000        
Increase in Regulatory Liability     5,000,000        
Renewable Base Tariff Energy Rate (R-BTER) Obligation $ 2,000,000            
Increase in Regulatory Asset     $ 3,000,000        
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Caesars Entertainment Corporation [Member]              
Public Utilities, General Disclosures [Line Items]              
Impact Fee Payment Term | number       6      
Total impact fee   $ 44,000,000          
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Stations Casinos LLC [Member]              
Public Utilities, General Disclosures [Line Items]              
Total impact fee $ 15,000,000            
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | General Rate Case [Member]              
Public Utilities, General Disclosures [Line Items]              
Public Utilities, Requested Rate Increase (Decrease), Amount       $ 29,000,000      
Public Utilities, Filed Rate Increase (Decrease), Percent       2.00%      
Public Utilities, Requested Rate Increase (Decrease), Amount       $ 0      
Public Utilities, Approved Rate Increase (Decrease), Amount       $ 26,000,000      
Public Utilities, Revenue Sharing, Percent       50.00%      
Public Utilities, Return on Equity, Percentage       10.00%      
Expense Related to Regulatory Rate Review       $ 44,000,000 28,000,000    
Expense Related to Regulatory Rate Review, Earnings Sharing       38,000,000      
Expense Related to Regulatory Rate Review, Carrying Charges       6,000,000      
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Tax Rate Reduction Rider [Member]              
Public Utilities, General Disclosures [Line Items]              
Public Utilities, Approved Rate Increase (Decrease), Amount       59,000,000      
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Energy Efficiency Rate Case [Member]              
Public Utilities, General Disclosures [Line Items]              
Customer Refund Liability, Current       $ 9,000,000 $ 10,000,000