Segment Information Segment Information - SPPC (Details) $ in Millions		3 Months Ended
		Mar. 31, 2018 USD ($) OperatingSegments TheNumberOfReportableSegments	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | OperatingSegments		8
Revenues		$ 4,440	$ 4,166
Operating income		871	967
Interest expense		466	458
Allowance for equity funds		21	17
Other, net		30	26
Income before income tax expense and equity income		285	591
Assets		$ 90,912		$ 90,208
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | TheNumberOfReportableSegments		2
Electric Domestic Regulated Revenue		$ 181	159
Gas Domestic Regulated Revenue		41	34
Revenues		222	193
Operating income		47	46
Interest expense		10	11
Allowance for equity funds		1	1
Other, net		2	1
Income before income tax expense and equity income		40	37
Assets		3,439		3,413
Sierra Pacific Power Company [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Electric Domestic Regulated Revenue		181	159
Revenues		181
Operating income		37	36
Assets		3,092		3,103
Sierra Pacific Power Company [Member] | Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Gas Domestic Regulated Revenue		41	34
Revenues		41
Operating income		10	$ 10
Assets		307		300
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 40		$ 10

[1] (1)Consists principally of cash and cash equivalents not included in either the regulated electric or regulated natural gas segments.