Recent Financing Transactions Recent Financing Transactions - NPC (Details) - Nevada Power Company [Member] - Subsequent Event [Member] $ in Millions	Apr. 30, 2018 USD ($)
Line of Credit [Member] \| Secured credit facility, $400 million, expiring June 2021 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 400
NVE Holdings [Member] \| NPC General and Refunding Mortgage Notes, Series BB [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 575
Debt Instrument, Interest Rate, Stated Percentage	2.75%
NVE Holdings [Member] \| NPC General and Refunding Mortgage Notes, Series O [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	$ 325
Debt Instrument, Interest Rate, Stated Percentage	6.50%
NVE Holdings [Member] \| NPC General and Refunding Mortgage Notes, Series S [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	$ 500
Debt Instrument, Interest Rate, Stated Percentage	6.50%

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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.

+ References

No definition available.

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- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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