Summary of Significant Accounting Policies - NPC - Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 571	$ 536
Energy Related Inventory, Other Fossil Fuel	273	352
Nevada Power Company [Member]
Inventory [Line Items]
Inventory, Raw Materials and Supplies, Gross	56	56
Energy Related Inventory, Other Fossil Fuel	$ 5	$ 3

Amount of fossil fuel included in inventory classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

+ References

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Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a)(4),(5))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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