Recent Financing Transactions Recent Financing Transactions - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	May 31, 2016	Apr. 30, 2016
Water facilities refunding revenue bonds, series 2016C, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 30
Water facilities refunding revenue bonds, series 2016D, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	25
Water facilities refunding revenue bonds, series 2016E, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	25
Gas facilities refunding revenue bonds, 1.500%, series 2016A, due 2031 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 59
Debt instrument, interest rate, stated percentage	1.50%
Gas and water facilities refunding revenue bonds, 3.000% series 2016B, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 60
Debt instrument, interest rate, stated percentage	3.00%
Water Facilities Refunding Revenue Bonds, Series 2016F, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 75
Water Facilities Refunding Revenue Bonds, Series 2016F, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	20
Pollution Control Refunding Revenue Bonds, 1.250%, Series A, due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 20
Debt instrument, interest rate, stated percentage	1.25%
Pollution Control Refunding Revenue Bonds, Series B, due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 30
General and Refunding Mortgage Bonds, Series V-1 [Member]
Debt Instrument [Line Items]
Troubled Debt Restructuring, Debtor, Subsequent Periods, Contingent Payments, Amount	80
General and Refunding Mortgage Bonds, Series V-2 [Member]
Debt Instrument [Line Items]
Troubled Debt Restructuring, Debtor, Subsequent Periods, Contingent Payments, Amount	214
General and Refunding Mortgage Bonds, Series V-3 [Member]
Debt Instrument [Line Items]
Troubled Debt Restructuring, Debtor, Subsequent Periods, Contingent Payments, Amount	50
Water Facilities Refunding Revenue Bonds Series, 2007A, due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount		$ 40
Water Facilities Refunding Revenue Bonds, Series 2007B, due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount		40
Gas Facilities Refunding Revenue Bonds, Series 2006A, due 2031 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount		59
Gas and Water Facilities Refunding Revenue Bonds, Series 2006C, due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount	$ 85
Pollution Control Revenue Bonds, Variable-Rate, Series 2006B due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount		75
Pollution Control Refunding Revenue Bonds, Series 2006, due 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount		50
Mortgage securities, 2.600%, Series U due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400
Debt instrument, interest rate, stated percentage		2.60%
Mortgage securities, 6.000%, Series M due 2016 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 450
Debt Instrument, Repurchased Face Amount		$ 450
Debt instrument, interest rate, stated percentage		6.00%