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Subsidiary Debt Subsidiary Debt - NPC - Annual Payment on Long-Term Debt (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months $ 3,431  
Long-term Debt, Maturities, Repayments of Principal in Year Two 2,103  
Long-term Debt, Maturities, Repayments of Principal in Year Three 1,674  
Long-term Debt, Maturities, Repayments of Principal in Year Four 886  
Long-term Debt, Maturities, Repayments of Principal in Year Five 1,838  
Long-term Debt, Maturities, Repayments of Principal after Year Five 25,444  
Par value 35,376  
Long-term Debt 35,193 $ 36,116
Nevada Power Company [Member]    
Debt Instrument [Line Items]    
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal in Next Twelve Months 898  
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal in Year Two 576  
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal in Year Three 76  
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal in Year Four 80  
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal in Year Five 75  
Long-term Debt and Capital and Financial Lease Obligations, Repayments of Principal Thereafter 2,069  
Par value 3,107  
Total Long-term Debt Maturities and Capital and Financial Leases Future Minimum Payments 3,774  
Debt Instrument, Unamortized Premium, Discount and Debt Issuance Cost 32  
Executory costs 92  
Capital and Financial Leases, Future Minimum Payments, Interest Included in Payments 575  
Long-term Debt 2,600 $ 2,581
Long-term Debt and Capital and Financial Lease Obligations, Including Current Maturities 3,075  
Nevada Power Company [Member] | Long-term Debt [Member]    
Debt Instrument [Line Items]    
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 823  
Long-term Debt, Maturities, Repayments of Principal in Year Two 500  
Long-term Debt, Maturities, Repayments of Principal in Year Three 0  
Long-term Debt, Maturities, Repayments of Principal in Year Four 0  
Long-term Debt, Maturities, Repayments of Principal in Year Five 0  
Long-term Debt, Maturities, Repayments of Principal after Year Five 1,309  
Par value 2,632  
Debt Instrument, Unamortized Premium, Discount and Debt Issuance Cost 32  
Executory costs 0  
Capital and Financial Leases, Future Minimum Payments, Interest Included in Payments 0  
Long-term Debt 2,600  
Nevada Power Company [Member] | Capital and Financial Lease Obligations [Member]    
Debt Instrument [Line Items]    
Capital and Financial Leases, Future Minimum Payments Due, Next Twelve Months 75  
Capital and Financial Leases, Future Minimum Payments Due in Two Years 76  
Capital and Financial Leases, Future Minimum Payments Due in Three Years 76  
Capital and Financial Leases, Future Minimum Payments Due in Four Years 80  
Capital and Financial Leases, Future Minimum Payments Due in Five Years 75  
Capital and Financial Leases, Future Minimum Payments Due Thereafter 760  
Capital and Financial Leases, Future Minimum Payments Due 1,142  
Debt Instrument, Unamortized Premium, Discount and Debt Issuance Cost 0  
Executory costs 92  
Capital and Financial Leases, Future Minimum Payments, Interest Included in Payments 575  
Capital and Financial Lease Obligations $ 475