XML 54 R44.htm IDEA: XBRL DOCUMENT v3.19.2
Financial Instruments - Narrative (Details)
3 Months Ended 9 Months Ended
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Bcf
MMcf
Jun. 30, 2018
USD ($)
Sep. 30, 2018
USD ($)
Derivative [Line Items]          
Net realized gain (loss) in AOCI $ (115,800,000)   $ (115,800,000)    
Net gain (loss) on settled interest rate agreements (1,400,000) $ (600,000) 2,600,000 $ 1,800,000  
Total long-term debt 3,685,000,000   3,685,000,000   $ 3,085,000,000
Unsecured 8.50% Senior Notes, due March 2019          
Derivative [Line Items]          
Total long-term debt $ 0   $ 0   $ 450,000,000
Gas Purchases | Not Designated as Hedging Instrument | Commodity contracts          
Derivative [Line Items]          
Hedging percent 33.00%   33.00%    
Energy measure | Bcf     18,900    
Minimum | Gas Purchases | Not Designated as Hedging Instrument | Commodity contracts          
Derivative [Line Items]          
Hedging percent 25.00%   25.00%    
Maximum | Gas Purchases | Not Designated as Hedging Instrument | Commodity contracts          
Derivative [Line Items]          
Hedging percent 50.00%   50.00%    
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap          
Derivative [Line Items]          
Notional amount $ 450,000,000   $ 450,000,000    
Net gain (loss) on settled interest rate agreements     90,100,000    
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap | Unsecured 8.50% Senior Notes, due March 2019          
Derivative [Line Items]          
Total long-term debt $ 450,000,000   $ 450,000,000    
Long | Gas Purchases | Not Designated as Hedging Instrument | Commodity contracts          
Derivative [Line Items]          
Energy measure | MMcf     16,784