Segment Information Segment Information - SPPC (Details) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($) OperatingSegments TheNumberOfReportableSegments	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | OperatingSegments		8
Revenues		$ 4,041	$ 4,221
Cost of sales		1,095	1,354
Operating income		953	930
Interest expense		473	472
Assets		$ 84,246		$ 83,618
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | TheNumberOfReportableSegments		2
Electric Domestic Regulated Revenue		$ 170	196
Gas Domestic Regulated Revenue		47	50
Revenues		217	246
Cost of sales		70	97
Cost of Purchased Oil and Gas		30	35
Cost of Sales		100	132
Gross Margin		117	114
Utilities Operating Expense, Maintenance and Operations		41	36
Utilities Operating Expense, Depreciation and Amortization		29	28
Operating income		41	43
Interest expense		16	15
Assets		3,500		3,487
Sierra Pacific Power Company [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Electric Domestic Regulated Revenue		170	196
Cost of sales		70	97
Gross Margin		100	99
Utilities Operating Expense, Maintenance and Operations		36	32
Utilities Operating Expense, Depreciation and Amortization		25	24
Operating income		33	37
Interest expense		14	14
Assets		3,031		3,060
Sierra Pacific Power Company [Member] | Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Gas Domestic Regulated Revenue		47	50
Cost of Purchased Oil and Gas		30	35
Gross Margin		17	15
Utilities Operating Expense, Maintenance and Operations		5	4
Utilities Operating Expense, Depreciation and Amortization		4	4
Operating income		8	6
Interest expense		2	$ 1
Assets		328		316
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 141		$ 111

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