Income Taxes - SPPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	$ (816)	$ (1,746)	$ (866)
Deferred Federal Income Tax Expense (Benefit)	1,310	2,296	1,306
Deferred State and Local Income Tax Expense (Benefit)	(53)	37	(247)
Deferred Income Tax Expense (Benefit)	1,274	2,344	1,000
Other Tax Expense (Benefit)	(8)	(9)	(4)
Income tax expense	450	589	130
Sierra Pacific Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	0	0	(2)
Deferred Federal Income Tax Expense (Benefit)	48	48	38
Deferred State and Local Income Tax Expense (Benefit)	0	0	(2)
Deferred Income Tax Expense (Benefit)	48	48	36
Other Tax Expense (Benefit)	(1)	(1)	(1)
Income tax expense	$ 47	$ 47	$ 33