Property, Plant and Equipment, Net Property, Plant and Equipment, Net - NPC(Details) - Nevada Power Company [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 6,861	$ 6,843
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	135	153
Public Utilities, Property, Plant and Equipment, Net	6,996	6,996
Regulated assets [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation or Processing	4,228	4,212
Public Utilities, Property, Plant and Equipment, Distribution	3,148	3,118
Public Utilities, Property, Plant and Equipment, Transmission	1,796	1,788
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	721	694
Public Utilities, Property, Plant and Equipment, Plant in Service, Excluding Construction Work In Progress	9,893	9,812
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	3,034	2,971
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	6,859	6,841
Unregulated operation [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 2	$ 2
Minimum [Member] | Regulated assets [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	25 years	25 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	20 years	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	45 years	45 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years	5 years
Minimum [Member] | Unregulated operation [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years	5 years
Maximum [Member] | Regulated assets [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	80 years	80 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	65 years	65 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	65 years	65 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	65 years	65 years
Maximum [Member] | Unregulated operation [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	65 years	65 years