Supplementary Information For Oil And Gas Producing Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014 ft3	Sep. 30, 2013 ft3	Sep. 30, 2012 ft3	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Reserve Quantities [Line Items]
Amount spent for developing proved undeveloped reserves	$ 179.9	$ 148.5	$ 216.6
Increase in Proved undeveloped (PUD) reserve	60,000,000,000	42,000,000,000
Percentage of PUD reserves to the total proved reserves	27.00%	29.00%	33.00%
New PUD reserve additions	290,000,000,000	221,000,000,000
Proved Undeveloped Reserves, Acquired	20,000,000,000
Proved Undeveloped Reserve (Volume)	512,000,000,000	452,000,000,000	410,000,000,000
PUD conversions to developed reserves	229,000,000,000	160,000,000,000
Proved Undeveloped Reserves, Removed	33,000,000,000
PUD revisions	12,000,000,000	(19,000,000,000)
Investment made to convert proved undeveloped reserves to developed reserves	180	149
Percentage of PUD reserves booked		51.00%	39.00%	33.00%	47.00%	19.00%
Conversion of undeveloped proved reserves to developed proved reserves	229,000,000,000	160,000,000,000
Arbitrary discount rate	10.00%
West Coast Region [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserves, Removed	9,000,000,000
Midway Sunset [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserves, Removed	1,501
Marcellus Shale Fields [Member]
Reserve Quantities [Line Items]
New PUD reserve additions	288,000,000,000	219,000,000,000
Proved Undeveloped Reserve (Volume)	504,000,000,000	432,000,000,000	381,000,000,000
Proved Undeveloped Reserves, Removed	24,000,000,000
Total PUD Reserve Additions Estimated In 2015 [Member]
Reserve Quantities [Line Items]
Amount to be spent on developing proved undeveloped reserves	$ 239
Conversion Of Undeveloped Proved Reserves To Developed Proved Reserves Including Revisions [Member]
Reserve Quantities [Line Items]
Conversion of undeveloped proved reserves to developed proved reserves	248,000,000,000	171,000,000,000