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Revenue - Narrative (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Type
Contract
Customer
Segment Reporting Information [Line Items]  
Number of customers | Customer 2,000,000
Number of customers party to contracts with rate components subject to negotiation (less than) | Customer 24
Southwest Gas Corporation  
Segment Reporting Information [Line Items]  
Number of types of services provided to customers 2
Centuri  
Segment Reporting Information [Line Items]  
Number of types of services provided to customers 3
Number of types of agreements with customers 2
Change in contract liability, revenue recognized | $ $ 4.2
Number of contracts with original duration more than one year | Contract 48