Regulatory Matters Regulatory Matters - NPC (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Regulatory Assets and Liabilities [Line Items]
Federal statutory income tax rate		21.00%	35.00%	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		21.00%	35.00%	21.00%	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] | Wynn Las Vegas LLC [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Impact Fee Credit				$ 3,000,000
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] | Public Utilities Commission, Nevada [Member] | General Rate Case [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
Nevada Power Company [Member] | Public Utilities Commission, Nevada [Member] | Tax Rate Reduction Rider [Member] | Scenario, Forecast [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						$ 59,000,000