Income Taxes - NPC - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	31.00%	0.00%	0.00%
Other, net	(2.00%)	(2.00%)	(2.00%)
Effective income tax rate	(22.00%)	14.00%	16.00%
Nevada Power Company [Member]
Income Tax Contingency [Line Items]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Merger Charges, Percent	1.00%	0.00%	1.00%
Other, net	1.00%	(1.00%)	0.00%
Effective income tax rate	38.00%	34.00%	36.00%
Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Contingency [Line Items]
Federal statutory income tax rate	21.00%
Tax Cuts and Jobs Act of 2017 [Member] \| Nevada Power Company [Member]
Income Tax Contingency [Line Items]
Federal statutory income tax rate	21.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	1.00%	0.00%	0.00%

Effective Income Tax Rate Reconciliation, Nondeductible Expense, Merger Charges, Percent

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(2))
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-Paragraph 12
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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

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-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
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-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the income tax rates.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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