Revenue from Contracts with Customers Revenue from Contracts with Customers - SPPC - Customer Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Unbilled Contracts Receivable	$ 624		$ 624		$ 665
Revenue from Contract with Customer, Excluding Assessed Tax	4,270		11,358
Operating revenue	5,637	$ 5,283	15,070	$ 14,003
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	149		460
Regulated Operation [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,844		10,297
Regulated Operation [Member] | Regulated retail electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,971		7,303
Sierra Pacific Power Company [Member]
Disaggregation of Revenue [Line Items]
Unbilled Contracts Receivable	51		51		$ 62
Operating revenue	239	$ 230	649	$ 600
Sierra Pacific Power Company [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	0		4
Sierra Pacific Power Company [Member] | Regulated electric
Disaggregation of Revenue [Line Items]
Operating revenue	225		575
Sierra Pacific Power Company [Member] | Regulated electric | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	0		3
Sierra Pacific Power Company [Member] | Regulated natural gas
Disaggregation of Revenue [Line Items]
Operating revenue	14		74
Sierra Pacific Power Company [Member] | Regulated natural gas | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	0		1
Sierra Pacific Power Company [Member] | Regulated Operation [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	239		645
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Regulated wholesale, transmission and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	13		36
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Regulated electric
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	225		572
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Regulated electric | Regulated wholesale, transmission and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	12		35
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Regulated natural gas
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	14		73
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Regulated natural gas | Regulated wholesale, transmission and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1		1
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	225		606
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	85		251
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	78		208
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	60		142
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2		5
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated electric | Regulated retail electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	212		534
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated electric | Regulated retail electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	76		203
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated electric | Regulated retail electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	75		190
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated electric | Regulated retail electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	59		136
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated electric | Regulated retail electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2		5
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated natural gas
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	13		72
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated natural gas | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	9		48
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated natural gas | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3		18
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated natural gas | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1		6
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled customer [Member] | Regulated natural gas | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0		0
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Distribution only service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1		3
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Distribution only service [Member] | Regulated electric | Regulated retail electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1		3
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Distribution only service [Member] | Regulated natural gas
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0		0
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled and distribution services only customer [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	226		609
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled and distribution services only customer [Member] | Regulated electric | Regulated retail electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	213		537
Sierra Pacific Power Company [Member] | Regulated Operation [Member] | Fully bundled and distribution services only customer [Member] | Regulated natural gas
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 13		$ 72