Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplemental Cash Flow Disclosure - NPC (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,265	$ 627
Restricted cash and cash equivalents	214	227
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,506	883	$ 1,544	$ 1,283
Nevada Power Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	81	111
Restricted cash and cash equivalents	9	10
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 90	$ 121	$ 423	$ 66