Property, Plant and Equipment, Net Property, Plant and Equipment, Net - NPC (Details) - Nevada Power Company [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 6,734		$ 6,804
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	96		73
Property, plant and equipment, net	6,830		6,877
Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Change in Accounting Estimates, Impact on Period of Change	5
Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation or Processing	3,702		3,707
Public Utilities, Property, Plant and Equipment, Distribution	3,373		3,314
Public Utilities, Property, Plant and Equipment, Transmission	1,864		1,860
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	820		793
Public Utilities, Property, Plant and Equipment, Plant in Service, Excluding Construction Work In Progress	9,759		9,674
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	3,026		2,871
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 6,733		6,803
Regulated Operation [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	30 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	45 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years
Regulated Operation [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	55 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	65 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	70 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	65 years
Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 1		$ 1
Unregulated Operation [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	45 years
Unregulated Operation [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	45 years
Scenario, Forecast [Member] | Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Change in Accounting Estimates, Impact on Future Periods		$ 7