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Supplementary Information For Oil And Gas Producing Activities (Proved Developed And Undeveloped Oil And Gas Reserve Quantities) (Details)
ft³ in Billions
12 Months Ended
Sep. 30, 2017
MMcf
MBbls
ft³
Sep. 30, 2016
MMcf
MBbls
ft³
Sep. 30, 2015
MMcf
MBbls
ft³
Sep. 30, 2014
MMcf
MBbls
Reserve Quantities [Line Items]        
Proved Undeveloped Reserve (Volume) | ft³ 612 543 827  
Natural Gas (Mmcf) [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves 1,674,575 2,142,128 1,682,884  
Extensions and Discoveries 386,657 185,347 633,360  
Revisions of Previous Estimates 90,849 (248,161) (34,441)  
Production Volume (157,088) (143,547) (139,563)  
Sales of Minerals in Place (21,873) (261,192) (112)  
Proved Developed and Undeveloped Reserves 1,973,120 1,674,575 2,142,128  
Proved Developed Reserves (Volume) 1,363,102 1,132,616 1,316,844 1,177,808
Proved Undeveloped Reserve (Volume) 610,018 541,959 825,284 505,076
Oil Mbbl [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves | MBbls 29,009 33,722 38,477  
Extensions and Discoveries | MBbls 674 530 533  
Revisions of Previous Estimates | MBbls 3,293 (2,247) (2,254)  
Production Volume | MBbls (2,740) (2,923) (3,034)  
Sales of Minerals in Place | MBbls (29) 73    
Proved Developed and Undeveloped Reserves | MBbls 30,207 29,009 33,722  
Proved Developed Reserves (Volume) | MBbls 29,799 28,771 33,370 37,255
Proved Undeveloped Reserve (Volume) | MBbls 408 238 352 1,222
West Coast Region [Member] | Natural Gas (Mmcf) [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves 43,124 49,346 58,822  
Extensions and Discoveries 8 0 0  
Revisions of Previous Estimates 6,369 (3,132) (6,317)  
Production Volume (2,995) (3,090) (3,159)  
Sales of Minerals in Place 0 0 0  
Proved Developed and Undeveloped Reserves 46,506 43,124 49,346  
Proved Developed Reserves (Volume) 46,506 43,124 49,346 57,907
Proved Undeveloped Reserve (Volume) 0 0 0 915
West Coast Region [Member] | Oil Mbbl [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves | MBbls 28,936 33,502 38,224  
Extensions and Discoveries | MBbls 674 530 533  
Revisions of Previous Estimates | MBbls 3,305 (2,201) (2,251)  
Production Volume | MBbls (2,736) (2,895) (3,004)  
Sales of Minerals in Place | MBbls 0 0    
Proved Developed and Undeveloped Reserves | MBbls 30,179 28,936 33,502  
Proved Developed Reserves (Volume) | MBbls 29,771 28,698 33,150 37,002
Proved Undeveloped Reserve (Volume) | MBbls 408 238 352 1,222
Appalachian Region [Member] | Natural Gas (Mmcf) [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves 1,631,451 2,092,782 1,624,062  
Extensions and Discoveries [1] 386,649 185,347 633,360  
Revisions of Previous Estimates 84,480 (245,029) (28,124)  
Production Volume [2] (154,093) (140,457) (136,404)  
Sales of Minerals in Place (21,873) (261,192) (112)  
Proved Developed and Undeveloped Reserves 1,926,614 1,631,451 2,092,782  
Proved Developed Reserves (Volume) 1,316,596 1,089,492 1,267,498 1,119,901
Proved Undeveloped Reserve (Volume) 610,018 541,959 825,284 504,161
Appalachian Region [Member] | Oil Mbbl [Member]        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves | MBbls 73 220 253  
Extensions and Discoveries | MBbls 0 0 0  
Revisions of Previous Estimates | MBbls (12) (46) (3)  
Production Volume | MBbls (4) (28) (30)  
Sales of Minerals in Place | MBbls (29) 73    
Proved Developed and Undeveloped Reserves | MBbls 28 73 220  
Proved Developed Reserves (Volume) | MBbls 28 73 220 253
Proved Undeveloped Reserve (Volume) | MBbls 0 0 0 0
Marcellus Shale Fields [Member]        
Reserve Quantities [Line Items]        
Proved Undeveloped Reserve (Volume) | ft³ 456 542 825  
Marcellus Shale Fields [Member] | Natural Gas (Mmcf) [Member]        
Reserve Quantities [Line Items]        
Extensions and Discoveries 181,000 179,000 598,000  
Production Volume (145,452) (135,598) (130,291)  
Percentage exceeding total reserve of production in proved developed and undeveloped reserves 15.00%      
[1] Extensions and discoveries include 598 Bcf (during 2015), 179 Bcf (during 2016) and 181 Bcf (during 2017), of Marcellus Shale gas in the Appalachian region.
[2] Extensions and discoveries include 598 Bcf (during 2015), 179 Bcf (during 2016) and 181 Bcf (during 2017), of Marcellus Shale gas in the Appalachian region.(