Impairment Charges (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Impairment of proved properties	$ 1,044	$ 458
Impairment of unproved properties	$ 59