Commitments and Contingencies - NPC - Legal (Details) - Nevada Power Company [Member]	1 Months Ended
	May. 31, 2014 MW	Sep. 30, 2015 power_purchase_agreements
Loss Contingencies [Line Items]
Number of Approved Renewable Power Purchase Agreements | power_purchase_agreements		2
210 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	210
300 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	300
272 Megawatts of Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	272
15 Megawatts of Solar Renewable Energy [Member]
Loss Contingencies [Line Items]
New Generation Capacity	15