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Debt - Narratives (Details)
1 Months Ended 3 Months Ended
Mar. 31, 2022
USD ($)
instrument
Nov. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
Mar. 31, 2022
USD ($)
instrument
Dec. 31, 2021
USD ($)
Debt Instrument [Line Items]          
Short-term debt $ 1,474,000,000     $ 1,474,000,000 $ 1,909,000,000
Debt instrument, term       364 days  
Loans Payable          
Debt Instrument [Line Items]          
Negative working capital condition 584,000,000     $ 584,000,000  
Term Loan Facility Due December 30, 2022 | Loans Payable          
Debt Instrument [Line Items]          
Borrowings outstanding under facility 1,160,000,000     1,160,000,000  
Debt instrument face amount   $ 1,600,000,000      
Debt instrument, term   364 days      
LIBOR          
Debt Instrument [Line Items]          
Borrowings outstanding under facility 2,170,000,000     2,170,000,000  
Southwest Gas Corporation          
Debt Instrument [Line Items]          
Short-term debt 250,000,000     250,000,000 $ 250,000,000
Southwest Gas Corporation | $250 Million Term Loan          
Debt Instrument [Line Items]          
Debt instrument face amount $ 250,000,000   $ 250,000,000 $ 250,000,000  
Debt covenant, ratio of funded debt to total capitalization 0.70     0.70  
Debt instrument, term     364 days    
Southwest Gas Corporation | Debentures | Notes, 4.05%, due 2032          
Debt Instrument [Line Items]          
Debt instrument face amount $ 600,000,000     $ 600,000,000  
Debt instrument interest rate 4.05%     4.05%  
Debt instrument discount rate 0.65%     0.65%  
Southwest Gas Corporation | Debentures | Notes, 3.875%, due 2022          
Debt Instrument [Line Items]          
Debt instrument face amount $ 250,000,000     $ 250,000,000  
Debt instrument interest rate 3.875%     3.875%  
Southwest Gas Corporation | SOFR | Minimum | $250 Million Term Loan          
Debt Instrument [Line Items]          
Debt, basis spread on variable rate 0.55%        
Southwest Gas Corporation | SOFR | Maximum | $250 Million Term Loan          
Debt Instrument [Line Items]          
Debt, basis spread on variable rate 1.00%        
Southwest Gas Corporation | Alternative base rate | $250 Million Term Loan          
Debt Instrument [Line Items]          
Debt, basis spread on variable rate 0.00%        
Southwest Gas Corporation | LIBOR          
Debt Instrument [Line Items]          
Borrowings outstanding under facility $ 0     $ 0  
Centuri | Centuri secured term loan facility          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 1,145,000,000     1,145,000,000  
Centuri | Centuri Secured Term Loan Facility And Revolving Credit Facility          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 1,545,000,000     1,545,000,000  
Borrowings outstanding under facility 1,122,000,000     1,122,000,000  
Debt secured by assets 2,400,000,000     $ 2,400,000,000  
Proceeds from facility $ 100,000,000        
MountainWest          
Debt Instrument [Line Items]          
Number of private placement | instrument 2     2  
MountainWest | Unsecured Debt          
Debt Instrument [Line Items]          
Debt instrument face amount $ 430,000,000     $ 430,000,000  
Aggregate carrying value 449,500,000     449,500,000  
$400 Million Credit Facility | Southwest Gas Corporation          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 400,000,000     400,000,000  
Line of credit designated as long term debt 150,000,000     150,000,000  
Line of credit designated for working capital purposes 250,000,000     250,000,000  
Long-term debt outstanding 0     0  
Short-term debt 0     $ 0  
$400 Million Credit Facility | Southwest Gas Corporation | SOFR          
Debt Instrument [Line Items]          
Debt, basis spread on variable rate       1.125%  
$400 Million Credit Facility | Southwest Gas Corporation | Alternative base rate          
Debt Instrument [Line Items]          
Debt, basis spread on variable rate       0.125%  
$100 Million Credit Facility          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 200,000,000     $ 200,000,000  
Borrowings outstanding under facility 69,000,000     69,000,000  
Centuri secured revolving credit facility | Centuri | Line of Credit          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 400,000,000     400,000,000  
Commercial Paper Program | Southwest Gas Corporation          
Debt Instrument [Line Items]          
Credit facility maximum borrowing capacity 50,000,000     50,000,000  
Borrowings outstanding under facility $ 0     $ 0