Income Taxes Income Tax Rate Change - NPC (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Rate Change [Line Items]
Federal statutory income tax rate	21.00%	35.00%	21.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Rate Change [Line Items]
Federal statutory income tax rate			21.00%
Deferred Income Tax Expense (Benefit)	$ 37
Current Income Tax Expense (Benefit)	37
Increase (Decrease) in Deferred Income Taxes	$ 14
Nevada Power Company [Member]
Income Tax Rate Change [Line Items]
Federal statutory income tax rate	21.00%	35.00%	21.00%	35.00%
Nevada Power Company [Member] | Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Rate Change [Line Items]
Federal statutory income tax rate			21.00%
Deferred Income Tax Expense (Benefit)	$ 12
Current Income Tax Expense (Benefit)	(12)
Increase (Decrease) in Deferred Income Taxes	5
Deferred Income Tax Charge [Member] | Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Rate Change [Line Items]
Increase in Regulatory Liability	14
Deferred Income Tax Charge [Member] | Nevada Power Company [Member] | Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Rate Change [Line Items]
Increase in Regulatory Liability	$ 5