Short-Term Debt and Credit Facilities - SPPC - Credit Facility (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	$ 11,030	$ 9,412
Short-term Debt	[1]	(2,286)	(3,214)
Line of Credit Facility, Remaining Borrowing Capacity	[1]	8,154	5,569
Sierra Pacific Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		250	250
Short-term Debt		(45)	0
Line of Credit Facility, Remaining Borrowing Capacity		$ 205	$ 250
Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt, Weighted Average Interest Rate		0.90%
Sierra Pacific Power Company [Member] | Secured credit facility, $250 million, expiring June 2022 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 250
Sierra Pacific Power Company [Member] | Secured credit facility, $250 million, expiring June 2022 [Member] | Line of Credit [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Debt To Capitalization Ratio		0.65

[1] The table does not include unused credit facilities and letters of credit for investments that are accounted for under the equity method.