Summary of Significant Accounting Policies - NPC - 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
Nevada Power Company [Member] | Allowance for Doubtful Accounts [Member]
Allowance for Doubtful Accounts [Line Items]
Beginning balance	13	14	$ 8
Charged to operating costs and expenses, net	16	16	14
Write-offs, net	17	17	8
Ending balance	$ 12	$ 13	$ 14