Acquisitions Acquisitions Asset (Details) a in Thousands, $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2019 USD ($) a	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) a acquisition	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired				$ 293	$ 25	$ 1,891
Number Of Acquisitions Closed | acquisition			2
Texas Delaware [Member]
Business Acquisition [Line Items]
OilandGasAcresUndevelopedandDevelopedNet | a	40
Payments to Acquire Businesses, Net of Cash Acquired	$ 106
Eagle Ford
Business Acquisition [Line Items]
OilandGasAcresUndevelopedandDevelopedNet | a	18
Payments to Acquire Businesses, Net of Cash Acquired	$ 191
Ownership Percentage				100.00%
Permian Basin [Member]
Business Acquisition [Line Items]
Gas and Oil Acres, Undeveloped and Developed, Net | a			91
Payments to Acquire Businesses, Net of Cash Acquired		$ 63
Permian Basin [Member] | BC Operating Transaction [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			$ 1,100
Permian Basin [Member] | Black Mountain Oil and Gas Transaction [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			$ 700