Risk Management and Hedging Activities Risk Management and Hedging Activities - NPC - Derivative Contract Volumes (Details) - Commodity Contract [Member] MWh in Millions, Dth in Millions	Dec. 31, 2016 Dth MWh	Dec. 31, 2015 Dth MWh
Electricity purchases (sales), net, in megawatt hours [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount | MWh	(5)	(10)
Natural gas purchases, in decatherms [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount | Dth	(271)	(317)
Nevada Power Company [Member] | Electricity purchases (sales), net, in megawatt hours [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount | MWh	(2)	(2)
Nevada Power Company [Member] | Natural gas purchases, in decatherms [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount | Dth	(114)	(126)