Share-Based Compensation - Equity-Classified Compensation (Details) - USD ($) $ in Millions		12 Months Ended
	May 05, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 18
Restricted stock and stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 22	$ 32	$ 39
Restricted stock and stock options | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		20	26	31
Restricted stock and stock options | Oil and natural gas properties
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		1	2	2
Restricted stock and stock options | Oil, natural gas and NGL production expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		1	3	5
Restricted stock and stock options | Exploration expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 0	$ 1	$ 1