Summary of Significant Accounting Policies - SPPC - Allowance for Doubtful Accounts (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Doubtful Accounts [Line Items]
Allowance for doubtful accounts	$ 2	$ 2	$ 2	$ 2
Accounts Receivable, Credit Loss Expense (Reversal)	2	1	1
Accounts Receivable, Allowance for Credit Loss, Writeoff	(2)	(1)	(1)
Allowance for doubtful accounts	$ 2	$ 2	$ 2