XML 94 R70.htm IDEA: XBRL DOCUMENT v3.10.0.1
Fair Value Measurements Fair Value Measurements Using Significant Unobservable Inputs (Details)
tons-per-year in Billions
 3 Months Ended
Dec. 31, 2018
USD ($)
tons-per-year
Dec. 31, 2017
USD ($)
Sep. 30, 2018
USD ($)
tons-per-year
Sep. 30, 2017
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Commodity contract derivatives $ 77,000,000   $ 72,000,000  
Commodity contract derivatives $ 10,000,000   $ 12,000,000  
Maximum        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value measurements tons per year | tons-per-year 0.8   0.8  
Price per ton $ 112.64   $ 112.24  
Minimum        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value measurements tons per year | tons-per-year 0.7   0.7  
Price per ton $ 12.25   $ 12.25  
Fair Value, Inputs, Level 3        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Commodity contract derivatives 63,000,000   59,000,000  
Commodity contract derivatives 0   1,000,000  
Commodity Contract Derivatives        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Balance 63,000,000 $ (73,000,000) $ 58,000,000 $ (67,000,000)
Net unrealized gains (losses) deferred as regulatory assets and liabilities $ 5,000,000 $ (6,000,000)