Risk Management and Hedging Activities - NPC - Derivative Contract Volumes (Details) - Commodity derivative [Member] MWh in Millions, Dth in Millions	Mar. 31, 2017 MWh Dth	Dec. 31, 2016 MWh Dth
Electricity purchases (in megawatt hours) [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | MWh	10	5
Natural gas purchases (in decatherms) [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | Dth	305	271
Nevada Power Company [Member] | Electricity purchases (in megawatt hours) [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | MWh	1	2
Nevada Power Company [Member] | Natural gas purchases (in decatherms) [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | Dth	147	114