Regulatory Matters Regulatory Matters - NPC (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Regulatory Assets and Liabilities [Line Items]
Federal statutory income tax rate	21.00%	35.00%		35.00%
Tax Cuts and Jobs Act of 2017 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Federal statutory income tax rate	21.00%
Nevada Power Company [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Federal statutory income tax rate		35.00%
Nevada Power Company [Member] | Tax Cuts and Jobs Act of 2017 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Federal statutory income tax rate	21.00%
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Caesars Entertainment Corporation [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Total impact fee	$ 44,000,000
Nevada Power Company [Member] | General Rate Case [Member] | Public Utilities Commission, Nevada [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Filed 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				$ 28,000,000
Scenario, Forecast [Member] | Nevada Power Company [Member] | Tax Rate Reduction Rider [Member] | Public Utilities Commission, Nevada [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 59,000,000