Income Taxes - NPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	$ (1,572)	$ (888)	$ (591)
Deferred Federal Income Tax Expense (Benefit)	1,438	431	165
Other Tax Expense (Benefit)	(3)	(6)	(6)
Income tax expense (benefit)	308	(598)	(583)
Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Current federal tax expense (benefit)	57	105	84
Deferred Federal Income Tax Expense (Benefit)	(10)	(31)	(13)
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	2
Other Tax Expense (Benefit)	0	(1)	(1)
Income tax expense (benefit)	$ 47	$ 73	$ 72