Commitments and Contingencies - NPC - Legal (Details) - Nevada Power Company [Member]	1 Months Ended		12 Months Ended
	Apr. 30, 2017 MW	Mar. 31, 2017 MW	Dec. 31, 2017 MW	Dec. 31, 2016 MW	Dec. 31, 2015 power_purchase_agreements MW	Dec. 31, 2014 MW
Loss Contingencies [Line Items]
Number of Approved Renewable Power Purchase Agreements | power_purchase_agreements					2
300 Megawatts of Coal Energy [Member]
Loss Contingencies [Line Items]
Coal-Fired Power Plant Capacity						300
257 Megawatts of Coal Energy [Member]
Loss Contingencies [Line Items]
Coal-Fired Power Plant Capacity		257
812 Megawatts of Coal Energy [Member]
Loss Contingencies [Line Items]
Coal-Fired Power Plant Capacity			812
272 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity						272
210 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity						210
15 Megawatts of Solar Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity					15
100 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity					100
100 Megawatts of Solar Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity				100
130 Megawatts of Natural Gas Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	130
Ownership Percentage Acquired	25.00%
54 Megawatts of Natural Gas Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	54
35 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity			35