Summary of Significant Accounting Policies - SPPC - Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts [Line Items]
Beginning balance	$ 31
Ending balance	33	$ 31
Sierra Pacific Power Company [Member] | Allowance for Doubtful Accounts [Member]
Allowance for Doubtful Accounts [Line Items]
Beginning balance	1	2	$ 1
Charged to operating costs and expenses, net	2	1	2
Write-offs, net	1	2	1
Ending balance	$ 2	$ 1	$ 2