Employee Benefit Plans - NPC - Amounts Payable (Details) - Nevada Power Company [Member] - NV Energy, Inc. [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Noncurrent Liabilities [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	$ 1	$ 1
Domestic Plan [Member] | Other Noncurrent Liabilities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	23	23
Domestic Plan [Member] | Other Noncurrent Liabilities [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	10	10
Domestic Plan [Member] | Other Current Liabilities [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Current	$ 1	$ 1