Commitments and Contingencies Commitments and Contingencies - NPC - Environmental Laws and Regulations (Details) - Nevada Power Company [Member] - MW	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
812 Megawatts of Coal Energy [Member]
Supply Commitment [Line Items]
Coal-Fired Power Plant Capacity	812
15 Megawatts of Solar Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity		15
100 Megawatts of Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity	100	100
272 Megawatts of Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity			272
210 Megawatts of Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity			210
35 Megawatts of Renewable Energy [Member]
Supply Commitment [Line Items]
New Generation Capacity	35