Recent Financing Transactions Recent Financing Transactions - NPC (Details) - Nevada Power Company [Member] - USD ($) $ in Millions	May 31, 2017	Jan. 31, 2017
Pollution Control Revenue Bonds, Variable-Rate, Series 2006 due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount		$ 38.0
Pollution Control Revenue Bonds, Variable-Rate, Series 2006A due 2032 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount		$ 38.0
NVE Holdings [Member] | Pollution Control Revenue Bonds, Variable-Rate, Series 2006 due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	$ 39.5
NVE Holdings [Member] | Pollution Control Revenue Bonds, Variable-Rate, Series 2006A due 2032 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	40.0
NVE Holdings [Member] | Pollution Control Refunding Revenue Bonds, 1.60%, Series 2017, Due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 40.0
Debt Instrument, Interest Rate, Stated Percentage	1.60%
NVE Holdings [Member] | NPC Pollution Control Refunding Revenue Bonds, 1.80%, Series 2017A, due 2032 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 40.0
Debt Instrument, Interest Rate, Stated Percentage	1.80%
NVE Holdings [Member] | NPC Pollution Control Refunding Revenue Bonds, 1.60%, Series 2017B, due 2039 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 13.0
Debt Instrument, Interest Rate, Stated Percentage	1.60%
NVE Holdings [Member] | NPC General and Refunding Mortgage Notes, Series AA, No. AA-1 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 40.0
NVE Holdings [Member] | NPC General and Refunding Mortgage Notes, Series AA, No. AA-2 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	53.0
NVE Holdings [Member] | Pollution Control Revenue Bonds, Variable-Rate, Series 2006B due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	$ 13.0