Short-Term Debt and Credit Facilities - NPC - 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
Nevada Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit		0.00	0.00
Nevada Power Company [Member] | Senior unsecured credit facility, $400 million, expiring June 2020 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 400,000,000
Debt to capitalization ratio		1.00
Nevada Power Company [Member] | Secured credit facility, $400 million, expiring June 2021 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 400,000,000
Debt to capitalization ratio		0.65
Sierra Pacific Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 250,000,000	250,000,000
Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit		0.00	$ 0.00
Sierra Pacific Power Company [Member] | Secured credit facility, $250 million, expiring June 2021 [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

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