Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplemental Cash Flow Disclosure - NPC (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,661	$ 627
Restricted cash and cash equivalents	181	227
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,857	883	$ 1,876	$ 1,283
Nevada Power Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	51	111
Restricted cash and cash equivalents	11	10
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 62	$ 121	$ 107	$ 66