Segment Information Segment Information - SPPC (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) OperatingSegments TheNumberOfReportableSegments	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | OperatingSegments				8
Revenues		$ 4,121	$ 4,448	$ 8,162	$ 8,669
Cost of sales		970	1,229	2,065	2,583
Operating income		854	1,007	1,807	1,937
Interest expense		468	476	941	948
Assets		84,607		$ 84,607		$ 83,618
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | TheNumberOfReportableSegments				2
Electric Domestic Regulated Revenue		162	201	$ 332	397
Gas Domestic Regulated Revenue		19	26	66	76
Revenues		181	227	398	473
Cost of sales		65	101	135	198
Cost of Purchased Oil and Gas		7	15	37	50
Cost of Sales		72	116	172	248
Gross Margin		109	111	226	225
Utilities Operating Expense, Maintenance and Operations		45	40	86	77
Utilities Operating Expense, Depreciation and Amortization		29	28	58	56
Operating income		28	37	69	80
Interest expense		14	15	30	30
Assets		3,450		3,450		3,487
Sierra Pacific Power Company [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Electric Domestic Regulated Revenue		162	201	332	397
Cost of sales		65	101	135	198
Gross Margin		97	100	197	199
Utilities Operating Expense, Maintenance and Operations		40	36	76	69
Utilities Operating Expense, Depreciation and Amortization		25	24	50	48
Operating income		26	34	59	71
Interest expense		13	14	27	28
Assets		3,059		3,059		3,060
Sierra Pacific Power Company [Member] | Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Gas Domestic Regulated Revenue		19	26	66	76
Cost of Purchased Oil and Gas		7	15	37	50
Gross Margin		12	11	29	26
Utilities Operating Expense, Maintenance and Operations		5	4	10	8
Utilities Operating Expense, Depreciation and Amortization		4	4	8	8
Operating income		2	3	10	9
Interest expense		1	$ 1	3	$ 2
Assets		316		316		316
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 75		$ 75		$ 111

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