Short-Term Debt and Credit Facilities - SPPC - Credit Facility (Details) $ in Millions		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	$ 6,345	$ 6,421
Line of Credit Facility, Amounts Supported	[1]	(457)	(415)
Line of Credit Facility, Remaining Borrowing Capacity	[1]	4,019	5,032
Sierra Pacific Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		250	250
Line of Credit Facility, Amounts Supported		(80)	0
Line of Credit Facility, Remaining Borrowing Capacity		170	$ 250
Sierra Pacific Power Company [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 250
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.