Acquisitions (Details) $ in Millions				1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 01, 2017 USD ($) a	May 01, 2017 USD ($) a Boe	Aug. 01, 2016 USD ($) a	Mar. 31, 2017 USD ($)	Jun. 30, 2017 a	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired | $						$ 1,828	$ 902
Business Combination, Consideration Transferred | $			$ 904
Permian Basin [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired | $				$ 63
Gas and Oil Acres, Undeveloped and Developed, Net | a					91,000
Permian Basin [Member] | Black Mountain Oil and Gas Transaction [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired | $	$ 700
Gas and Oil Acres, Undeveloped and Developed, Net | a	21,000
Permian Basin [Member] | BC Operating Transaction [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired | $		$ 1,100
Gas and Oil Acres, Undeveloped and Developed, Net | a		70,000
Production, Barrels of Oil Equivalents | Boe		5,000
Northern Delaware - Permian Basin [Member] | BC Operating Transaction [Member]
Business Acquisition [Line Items]
Gas and Oil Acres, Undeveloped and Developed, Net | a					70,000
Anadarko Basin STACK Play [Member]
Business Acquisition [Line Items]
Gas and Oil Acres, Undeveloped and Developed, Net | a			61,000