Income Taxes - NPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	$ (687)	$ (816)	$ (1,746)
Deferred federal income tax expense (benefit)	1,098	1,274	2,344
Other Tax Expense (Benefit)	(8)	(8)	(9)
Income tax expense	403	450	589
Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	68	0	0
Deferred federal income tax expense (benefit)	79	163	131
Other Tax Expense (Benefit)	(1)	(1)	(1)
Income tax expense	$ 146	$ 162	$ 130