Income Taxes - NPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	$ (591)	$ (573)	$ (687)
Deferred Income Tax Expense (Benefit)	14	26	1,098
Other Tax Expense (Benefit)	(6)	(7)	(8)
Income tax (benefit) expense	(583)	(554)	403
Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	84	62	68
Deferred Income Tax Expense (Benefit)	(13)	95	79
Unrecognized Tax Benefits, Period Increase (Decrease)	2	0	0
Other Tax Expense (Benefit)	(1)	(1)	(1)
Income tax (benefit) expense	$ 72	$ 156	$ 146