Income Taxes Income Taxes - NPC - Tax Reform (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Income Tax Expense (Benefit) [Line Items]
Federal statutory income tax rate			21.00%	35.00%	35.00%
Deferred Tax Liabilities, Net			$ 9,047	$ 8,242
Regulatory Liabilities			7,506	7,511
Deferred Income Tax Expense (Benefit)			14	26	$ 1,098
Deferred Income Tax Charge [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Regulatory Liabilities	[1]		$ 3,923	$ 4,143
Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Federal statutory income tax rate			21.00%	35.00%	35.00%
Deferred Tax Liabilities, Net			$ 749	$ 767
Regulatory Liabilities			1,186	1,121
Deferred Income Tax Expense (Benefit)			$ (13)	95	$ 79
Tax Cuts and Jobs Act of 2017 [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Federal statutory income tax rate			21.00%
Deferred Tax Liabilities, Net	[2]		$ 7,115
Deferred Income Tax Expense (Benefit)			68
Increase (Decrease) in Deferred Income Taxes			(27)
Tax Cuts and Jobs Act of 2017 [Member] | Deferred Income Tax Charge [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Regulatory Liabilities	[2]		$ 5,950
Deferred Income Tax Expense (Benefit)	[2]	$ 1,150
Tax Cuts and Jobs Act of 2017 [Member] | Nevada Power Company [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Federal statutory income tax rate			21.00%
Deferred Tax Liabilities, Net	[2]			787
Deferred Income Tax Expense (Benefit)			$ 12
Increase (Decrease) in Deferred Income Taxes			$ (5)
Tax Cuts and Jobs Act of 2017 [Member] | Nevada Power Company [Member] | Deferred Income Tax Charge [Member]
Components of Income Tax Expense (Benefit) [Line Items]
Regulatory Liabilities	[2]			$ 792

[1] (1)Amounts primarily represent income tax liabilities related to the federal tax rate change from 35% to 21% that are probable to be passed on to customers, offset by income tax benefits related to certain property-related basis differences and other various differences that were previously passed on to customers and will be included in regulated rates when the temporary differences reverse. See Note 11 for further discussion of 2017 Tax Reform impacts.

[2] (1)Amounts primarily represent income tax liabilities related to the federal tax rate change from 35% to 21% that are probable to be passed on to customers, offset by income tax benefits related to accelerated tax depreciation and certain property-related basis differences that were previously passed on to customers and will be included in regulated rates when the temporary differences reverse. Amount includes regulatory liabilities with an indeterminate life of $82 million as of December 31, 2018. See Note 9 for further discussion of 2017 Tax Reform impacts.