Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplemental Cash Flow Disclosure - SPPC (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,016	$ 935
Restricted cash and cash equivalents	358	327
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,402	1,283	$ 1,459	$ 1,003
Sierra Pacific Power Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	71	4
Restricted cash and cash equivalents	4	4
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 75	$ 8	$ 33	$ 60