Supplemental Oil And Gas Disclosures (Summary Of Changes In Reserves - United States) (Details) ft³ in Billions	12 Months Ended
	Dec. 31, 2016 MBbls ft³	Dec. 31, 2015 MBbls ft³	Dec. 31, 2014 MBbls ft³
Reserve Quantities [Line Items]
Proved reserves, beginning of year | ft³	6,215	10,747	6,976
Revisions of previous estimates | ft³	(354)	(4,083)	543
Extensions, discoveries and other additions | ft³	282	592	1,693
Production | ft³	(875)	(976)	(768)
Acquisition of reserves in place | ft³		115	2,303
Disposition of reserves in place | ft³	(15)	(180)
Proved reserves, end of year | ft³	5,253	6,215	10,747
United States [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved reserves, beginning of year | ft³	5,917	9,809	6,974
Revisions of previous estimates | ft³	(446)	(3,458)	542
Extensions, discoveries and other additions | ft³	198	546	1,692
Production | ft³	(788)	(899)	(766)
Acquisition of reserves in place | ft³		97	1,367
Disposition of reserves in place | ft³	(15)	(178)
Proved reserves, end of year | ft³	4,866	5,917	9,809
Proved developed reserves:
Beginning of year | ft³	5,474	5,675	4,237
End of year | ft³	4,789	5,474	5,675
Proved undeveloped reserves:
Beginning of year | ft³	443	4,134	2,737
End of year | ft³	77	443	4,134
United States [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved reserves, beginning of year	8,753	37,615	373
Revisions of previous estimates	1,564	(28,394)	(14)
Extensions, discoveries and other additions	2,417	1,367	250
Production	(2,192)	(2,265)	(235)
Acquisition of reserves in place		525	37,246
Disposition of reserves in place	(19)	(95)	(5)
Proved reserves, end of year	10,523	8,753	37,615
Proved developed reserves:
Beginning of year	8,753	7,445	372
End of year	10,523	8,753	7,445
Proved undeveloped reserves:
Beginning of year		30,170	1
End of year			30,170
United States [Member] | NGL [Member]
Reserve Quantities [Line Items]
Proved reserves, beginning of year	40,947	118,699
Revisions of previous estimates	13,794	(75,664)	66
Extensions, discoveries and other additions	11,576	6,274	48
Production	(12,372)	(10,702)	(231)
Acquisition of reserves in place		2,340	118,816
Disposition of reserves in place	(14)
Proved reserves, end of year	53,931	40,947	118,699
Proved developed reserves:
Beginning of year	40,947	38,632
End of year	53,931	40,947	38,632
Proved undeveloped reserves:
Beginning of year		80,067
End of year			80,067