Natural Gas And Oil Producing Activities (Unaudited) (Results Of Operations For Oil And Gas Producing Activities Disclosure) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Natural Gas And Oil Producing Activities (Unaudited) [Abstract]
Sales	$ 2,862	$ 2,404	$ 1,963
Production (lifting) costs	(776)	(629)	(505)
Depreciation, depletion and amortization	(884)	(735)	(765)
Impairment of natural gas and oil properties			(1,940)
Results of operations - income before income taxes	1,202	1,040	(1,247)
Provision (benefit) for income taxes	457	416	(497)
Results of operations	$ 745	$ 624	$ (750)