Short-Term Debt and Credit Facilities - NPC - Credit Facility (Details)		Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	$ 6,421,000,000	$ 6,696,000,000
Nevada Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		400,000,000
Long-term Line of Credit		0	0
Nevada Power Company [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit		$ 0	$ 6,000,000
Nevada Power Company [Member] | Senior unsecured credit facility, $400 million, expiring March 2018 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt to capitalization ratio		0.68	0.68

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