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Subsequent Events (Details) - Subsequent Event [Member] - USD ($)
$ in Millions
3 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Aug. 16, 2018
Subsequent Event [Line Items]      
Senior notes     $ 400
Early Repayment of Senior Debt   $ 415  
Gain (Loss) on Extinguishment of Debt   $ 7  
Proceeds from formation of new mineral relationship $ 220    
Combined per year acquisitions of additional mineral interests $ 125