Segment Information Segment Information - SPPC (Details) $ in Millions		3 Months Ended
		Mar. 31, 2019 USD ($) OperatingSegments TheNumberOfReportableSegments	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | OperatingSegments		8
Operating revenue		$ 4,610	$ 4,440
Operating income		919	871
Interest expense		477	466
Allowance for equity funds		32	21
Other, net		35	30
Income before income tax expense and equity income		487	285
Assets		$ 94,545		$ 92,189
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | TheNumberOfReportableSegments		2
Operating revenue		$ 219	222
Operating income		37	47
Interest expense		12	10
Allowance for equity funds		1	1
Other, net		2	2
Income before income tax expense and equity income		28	40
Assets		3,617		3,569
Sierra Pacific Power Company [Member] | Regulated electric
Segment Reporting Information [Line Items]
Regulated Operating Revenue		182	181
Operating revenue		182	181
Operating income		29	37
Assets		3,227		3,177
Sierra Pacific Power Company [Member] | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Gas		37	41
Operating revenue		37	41
Operating income		8	$ 10
Assets		316		314
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 74		$ 78

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