Commitments and Contingencies Commitments and Contingencies - NPC - Environmental Laws and Regulations (Details) - Nevada Power Company [Member] - MW	1 Months Ended		9 Months Ended	12 Months Ended
	Apr. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
300 Megawatts of Coal Energy [Member]
Supply Commitment [Line Items]
Coal-Fired Power Plant Capacity						300
257 Megawatts of Coal Energy [Member]
Supply Commitment [Line Items]
Coal-Fired Power Plant Capacity		257
812 Megawatts of Coal Energy [Member]
Supply Commitment [Line Items]
Coal-Fired Power Plant Capacity			812
272 Megawatts of Natural Gas Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity						272
210 Megawatts of Natural Gas Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity						210
15 Megawatts of Solar Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity					15
100 Megawatts of Solar Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity				100	100
130 Megawatts of Natural Gas Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity	130
Ownership Percentage Acquired	25.00%
54 Megawatts of Natural Gas Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity	54
35 Megawatts of Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity			35