Employee Benefit Plans - SPPC - Amounts Payable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 6
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	34
Sierra Pacific Power Company [Member] | Domestic Plan [Member] | Other Noncurrent Liabilities [Member] | NV Energy, Inc. [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	6
Liability, Defined Benefit Plan, Noncurrent	0	$ 2
Employer contributions	6
Sierra Pacific Power Company [Member] | Domestic Plan [Member] | Other Noncurrent Liabilities [Member] | NV Energy, Inc. [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	8	8
Sierra Pacific Power Company [Member] | Domestic Plan [Member] | Other Noncurrent Liabilities [Member] | NV Energy, Inc. [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	13	20
Employer contributions	6
Sierra Pacific Power Company [Member] | Domestic Plan [Member] | Other Assets [Member] | NV Energy, Inc. [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets for Plan Benefits, Defined Benefit Plan		0
Sierra Pacific Power Company [Member] | Domestic Plan [Member] | Other Current Liabilities [Member] | NV Energy, Inc. [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Current	$ 1	$ 1