Basis of Presentation - Statements of Operations Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Income From Equity Method Investees and Other
Income from Equity Method Investees	$ 47		$ 42
Sales of Purchased Oil and Gas	53		0
Midstream Services Revenues – Third Party	13		0
Total	113	$ 42	$ 42
Production Expense
Lease Operating Expense	155	139
Production and Ad Valorem Taxes	54	41
Gathering, Transportation and Processing Expense	95	119
Other Royalty Expense	17	4
Total	321	303
Exploration Expense
Leasehold Impairment and Amortization	0	18
Seismic, Geological and Geophysical	11	5
Staff Expense	14	13
Other	10	6
Total	35	42
Other Operating Expense, Net
Marketing Expense	5	19
Purchased Oil and Gas	57	0
Other, Net	(8)	(10)
Total	70	29
Other Non-Operating Expense (Income), Net
Loss on Investment in Tamar Petroleum Ltd., Net	15	0
Other	(2)	(1)
Total	13	$ (1)
Loss from change in fair value	29
Dividend income	14
Saddle Butte
Other Operating Expense, Net
Purchased Oil and Gas	$ 5