Property, Plant and Equipment, Net Property, Plant and Equipment, Net - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 2,750	$ 2,715
Public Utilities, Property, Plant and Equipment, Net	2,862	2,822
Common Facilities [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	112	107
Public Utilities, Property, Plant and Equipment, Net	2,862	2,822
Regulated assets [Member] | Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation or Processing	1,140	1,137
Public Utilities, Property, Plant and Equipment, Distribution	1,445	1,417
Public Utilities, Property, Plant and Equipment, Transmission	782	771
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	$ 182	$ 164
Regulated assets [Member] | Electricity Generation Plant, Non-Nuclear [Member] | Minimum [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	50 years	50 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years	5 years
Regulated assets [Member] | Electricity Generation Plant, Non-Nuclear [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	60 years	60 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	100 years	100 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	100 years	100 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	70 years	70 years
Regulated assets [Member] | Natural Gas Processing Plant [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Distribution	$ 388	$ 381
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	$ 14	$ 15
Regulated assets [Member] | Natural Gas Processing Plant [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	35 years	35 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years	5 years
Regulated assets [Member] | Natural Gas Processing Plant [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	70 years	70 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	70 years	70 years
Regulated assets [Member] | Common Facilities [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Common	$ 290	$ 267
Public Utilities, Property, Plant and Equipment, Plant in Service, Excluding Construction Work In Progress	4,241	4,152
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	1,496	1,442
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 2,745	$ 2,710
Regulated assets [Member] | Common Facilities [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Common, Useful Life	5 years	5 years
Regulated assets [Member] | Common Facilities [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Common, Useful Life	70 years	70 years
Unregulated asset [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Net, Excluding Construction Work In Progress	$ 5	$ 5
Unregulated asset [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	70 years	70 years
Unregulated asset [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	70 years	70 years
Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Change in Accounting Estimates, Impact on Future Periods			$ 9
Change in Accounting Estimate, Amount Deferred to Future Periods		$ 7