Summary of Significant Accounting Policies - NPC - Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 786	$ 616
Nevada Power Company [Member]
Inventory [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 69	$ 62

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

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=120391452&loc=d3e13212-122682

Name:	us-gaap_InventoryRawMaterialsAndSupplies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant