Natural Gas And Oil Producing Activities (Schedule Of Analysis Of Changes In Standardized Measure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Natural Gas And Oil Producing Activities [Abstract]
Standardized measure, beginning of year	$ 7,543	$ 3,736	$ 2,051
Sales and transfers of natural gas and oil produced, net of production costs	(1,082)	(2,084)	(1,774)
Net changes in prices and production costs	(8,075)	1,192	1,853
Extensions, discoveries, and other additions, net of future production and development costs	162	1,049	1,454
Acquisition of reserves in place	28	1,897	5
Sales of reserves in place	(244)
Revisions of previous quantity estimates	(1,385)	622	349
Accretion of discount	946	513	232
Net change in income taxes	1,915	(522)	(1,120)
Changes in estimated future development costs	2,007	110	(196)
Previously estimated development costs incurred during the year	875	815	223
Changes in production rates (timing) and other	(273)	215	659
Standardized measure, end of year	$ 2,417	$ 7,543	$ 3,736