Summary of Significant Accounting Policies - SPPC - Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Doubtful Accounts [Line Items]
Beginning balance	$ 37
Ending balance	31	$ 37
Sierra Pacific Power Company [Member] | Allowance for Doubtful Accounts [Member]
Allowance for Doubtful Accounts [Line Items]
Beginning balance	2	1	$ 1
Charged to operating costs and expenses, net	1	2	2
Write-offs, net	2	1	2
Ending balance	$ 1	$ 2	$ 1