Segment Information Segment Information - SPPC (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) OperatingSegments TheNumberOfReportableSegments	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | OperatingSegments				8
Operating revenue		$ 5,637	$ 5,283	$ 15,070	$ 14,003
Operating income		1,523	1,640	3,366	3,652
Interest expense		453	464	1,380	1,379
Allowance for equity funds		30	24	75	59
Other, net		19	(17)	50	8
Income before income tax expense and equity income		1,423	1,232	1,904	2,467
Assets		91,862		$ 91,862		$ 90,208
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | TheNumberOfReportableSegments				2
Operating revenue		239	230	$ 649	600
Operating income		56	74	122	156
Interest expense		12	11	33	33
Allowance for Funds Used During Construction, Capitalized Interest		0	1	1	1
Allowance for equity funds		1	1	3	2
Other, net		3	3	8	5
Income before income tax expense and equity income		48	68	101	131
Assets		3,516		3,516		3,413
Sierra Pacific Power Company [Member] | Regulated electric
Segment Reporting Information [Line Items]
Regulated Operating Revenue		225	215	575	534
Operating revenue		225		575
Operating income		56	71	111	141
Assets		3,131		3,131		3,103
Sierra Pacific Power Company [Member] | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Gas		14	15	74	66
Operating revenue		14		74
Operating income		0	$ 3	11	$ 15
Assets		300		300		300
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 85		$ 85		$ 10

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