Natural Gas And Oil Producing Activities (Standardized Measure Of Discounted Future Cash Flows Relating To Proved Reserves Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Natural Gas And Oil Producing Activities [Abstract]
Future cash inflows	$ 11,887	$ 41,812	$ 22,624
Future production costs	(7,376)	(16,477)	(8,896)
Future development costs	(792)	(5,750)	(3,626)
Future income tax expense		(4,743)	(3,223)
Future net cash flows	3,719	14,842	6,879
10% annual discount for estimated timing of cash flows	(1,302)	(7,299)	(3,143)
Standardized measure of discounted future net cash flows	$ 2,417	$ 7,543	$ 3,736	$ 2,051
Annual discount for estimated timing of cash flows percent	10.00%	10.00%	10.00%