Employee Benefit Plans - NPC - Amounts Payable (Details) - Nevada Power Company [Member] - Domestic Plan [Member] - NV Energy, Inc. [Member] - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Other Noncurrent Liabilities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	$ 23	$ 23
Other Noncurrent Liabilities [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	10	10
Other Noncurrent Liabilities [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Noncurrent	0	1
Other Current Liabilities [Member] | Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Current	1	1
Other Assets [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	$ 1	$ 0