Natural Gas And Oil Producing Activities (Results Of Operations For Oil And Gas Producing Activities Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Natural Gas And Oil Producing Activities [Abstract]
Sales	$ 2,074	$ 2,862	$ 2,404
Production (lifting) costs	(989)	(776)	(629)
Depreciation, depletion and amortization	(1,028)	(884)	(735)
Impairment of natural gas and oil properties	(6,950)
Results of operations - income before income taxes	(6,893)	1,202	1,040
Provision (benefit) for income taxes	(2,619)	457	416
Results of operations	$ (4,274)	$ 745	$ 624