Income Taxes - NPC - 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)	1,274	2,344	1,000
Other Tax Expense (Benefit)	(8)	(9)	(4)
Income tax expense	450	589	130
Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	0	0	(1)
Deferred federal income tax expense (benefit)	163	131	96
Other Tax Expense (Benefit)	(1)	(1)	(1)
Income tax expense	$ 162	$ 130	$ 94