Supplemental Oil and Gas Disclosures (Schedule of Analysis of Changes in Standardized Measure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure, beginning of year	$ 5,999	$ 5,562	$ 1,665
Sales and transfers of natural gas and oil produced, net of production costs	(923)	(1,564)	(1,191)
Net changes in prices and production costs	(3,510)	2,162	1,963
Extensions, discoveries, and other additions, net of future production and development costs	234	335	1,715
Increase Due to Purchases of Minerals in Place	0	0	0
Sales of reserves in place	(2)	(2,022)	0
Revisions of previous quantity estimates	152	361	1,721
Net change in income taxes	491	(304)	(222)
Changes in estimated future development costs	621	(166)	(6)
Previously estimated development costs incurred during the year	704	536	55
Changes in production rates (timing) and other	(718)	521	(304)
Accretion of discount	652	578	166
Standardized measure, end of year	$ 3,700	$ 5,999	$ 5,562