Summary of Significant Accounting Policies (Schedule of Revenue from Contracts with Customers) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	$ 2,290	$ 1,367
Oil, Gas and NGL Sales [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	1,788	807
Oil, Gas and NGL Sales [Member] | Oil [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	1,357	662
Oil, Gas and NGL Sales [Member] | Gas [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	207	70
Oil, Gas and NGL Sales [Member] | NGL [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	224	75
Marketing and Midstream Revenues [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	502	560
Marketing and Midstream Revenues [Member] | Oil [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	209	329
Marketing and Midstream Revenues [Member] | Gas [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	118	94
Marketing and Midstream Revenues [Member] | NGL [Member]
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	$ 175	$ 137