Short-Term Debt and Credit Facilities - SPPC - Credit Facility (Details)		Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	$ 9,114,000,000	$ 9,051,000,000
Line of Credit Facility, Amounts Supported	[1]	(543,000,000)	(594,000,000)
Line of Credit Facility, Remaining Borrowing Capacity	[1]	6,055,000,000	3,969,000,000
Sierra Pacific Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		250,000,000	250,000,000
Line of Credit Facility, Amounts Supported		(80,000,000)	(80,000,000)
Line of Credit Facility, Remaining Borrowing Capacity		170,000,000	170,000,000
Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit		0.00	$ 0.00
Secured credit facility, $250 million, expiring June 2021 [Member] | Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 250,000,000
Debt to capitalization ratio		0.65
Minimum [Member] | Secured credit facility, $250 million, expiring June 2021 [Member] | Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt to capitalization ratio		0.65
Maximum [Member] | Secured credit facility, $250 million, expiring June 2021 [Member] | Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt to capitalization ratio		1.00

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