Segment Information - SPPC (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) OperatingSegments TheNumberOfReportableSegments	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | OperatingSegments		8
Revenues		$ 17,880	$ 17,326	$ 12,635
Cost of sales		5,079	5,732	3,799
Operating income (loss)		4,328	4,046	2,835
Income tax expense		450	589	130
Payments to Acquire Property, Plant, and Equipment		5,875	6,555	4,307
Assets		$ 83,618	81,816	69,591
Sierra Pacific Power Company [Member]
Segment Reporting Information [Line Items]
Number of Reportable Segments | TheNumberOfReportableSegments		2
Electric Domestic Regulated Revenue		$ 810	779	747
Gas Domestic Regulated Revenue		137	125	106
Revenues		947	904	853
Cost of sales		374	361	292
Cost of Purchased Oil and Gas		84	76	56
Cost of Sales		458	437	348
Gross Margin		489	467	505
Operations and maintenance		163	158	197
Utilities Operating Expense, Depreciation and Amortization		113	105	123
Operating income (loss)		184	178	140
Interest expense, net of borrowed funds		61	61	61
Income tax expense		47	47	33
Payments to Acquire Property, Plant, and Equipment		252	186	139
Assets		3,487	3,336	3,311
Sierra Pacific Power Company [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Electric Domestic Regulated Revenue		810	779	747
Cost of sales		374	361	292
Electric Domestic Regulated Gross Margin		436	418	455
Electricity, Utilities Operating Expense, Maintenance and Operations		146	140	176
Utilities Operating Expense, Depreciation and Amortization		96	90	106
Operating income (loss)		168	165	134
Electric, Interest Expense, net of allowance for borrowed funds		56	57	56
Income tax expense		43	43	32
Payments to Acquire Property, Plant, and Equipment		229	168	125
Assets		3,060	2,984	2,905
Sierra Pacific Power Company [Member] | Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Gas Domestic Regulated Revenue		137	125	106
Cost of Purchased Oil and Gas		84	76	56
Gas Domestic Regulated Gross Margin		53	49	50
Gas, Utilities Operating Expense, Maintenance and Operations		17	18	21
Utilities Operating Expense, Depreciation and Amortization		17	15	17
Operating income (loss)		16	13	6
Gas, Interest Expense, net of allowance for borrowed funds		5	4	5
Income tax expense		4	4	1
Payments to Acquire Property, Plant, and Equipment		23	18	14
Assets		316	322	329
Sierra Pacific Power Company [Member] | Regulated common assets [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ 111	$ 30	$ 77

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