Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 592	$ 990
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	353	551
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	239	439
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	344	542
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	548	941
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	300	493
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(9)	(9)
Intersegment Revenues | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	309	502
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	248	430
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	239	421
Gas sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Gas sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	(9)	(9)
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	52	39
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	52	39
Oil sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Oil sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	50	81
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	50	81
NGL sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
NGL sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	239	438
Marketing | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Marketing | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	548	940
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	309	502
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	3	2
Other | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	3	1
Other | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	1
Other | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0