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Risk Management Activities and Derivative Transactions Counterparty Credit Risk (Details)
$ in Millions
 3 Months Ended
Dec. 31, 2021
USD ($)
Customers
Sep. 30, 2021
USD ($)
Derivative    
Accounts Receivable, before Allowance for Credit Loss, Current | $ $ 1,310 $ 1,480
Total derivatives not subject to master netting or similar arrangement | $ $ 111 $ 250
Two Largest Customer Percentage of Total Operating Revenue 1600.00%  
Moody's, A1 Rating [Member]    
Derivative    
Banking Counterparties Credit Rating A2  
Natural Gas Banking Counterparties Credit Rating A1  
Moody's, Caa1 Rating [Member]    
Derivative    
Natural Gas Banking Counterparties Credit Rating B1  
Credit of Customers    
Derivative    
Number of customers that represent the percent of sales | Customers 2  
Number of customers that represent the percent of sales | Customers 2