Supplemental Oil and Gas Disclosures - Proved Reserve Data (Detail)	12 Months Ended
	Dec. 31, 2014 MBbls	Dec. 31, 2013 MBbls	Dec. 31, 2012 MBbls	Dec. 31, 2011 MBbls
Reserve Quantities [Line Items]
Proved developed reserves	1,651,291	1,832,936	1,981,945	1,992,327
Proved undeveloped reserves	744,979	813,480	869,734	997,527
Beginning balance	2,646,416	2,851,679	2,989,854
Extensions, discoveries and other additions	313,095	389,336	372,393
Purchase of minerals in-place	21,712	5,976	73,457
Revisions of previous estimates	11,404	32,539	(298,712)
Production	(238,831)	(277,683)	(284,997)
Sale of properties	(357,526)	(355,431)	(316)
Ending balance	2,396,270	2,646,416	2,851,679
United States [Member]
Reserve Quantities [Line Items]
Proved developed reserves	897,422	976,795	1,021,610	905,069
Proved undeveloped reserves	336,670	370,566	402,677	385,013
Beginning balance	1,347,361	1,424,287	1,290,082
Extensions, discoveries and other additions	138,413	253,578	217,598
Purchase of minerals in-place	21,712	273	68,486
Revisions of previous estimates	11,662	13,482	(38,172)
Production	(106,225)	(121,074)	(113,461)
Sale of properties	(178,831)	(223,185)	(246)
Ending balance	1,234,092	1,347,361	1,424,287
Canada [Member]
Reserve Quantities [Line Items]
Proved developed reserves	258,848	322,362	390,800	456,569
Proved undeveloped reserves	155,028	139,509	150,113	307,724
Beginning balance	461,871	540,913	764,293
Extensions, discoveries and other additions	74,666	74,107	68,612
Purchase of minerals in-place			614
Revisions of previous estimates	(2,800)	18,274	(247,811)
Production	(28,313)	(39,177)	(44,725)
Sale of properties	(91,548)	(132,246)	(70)
Ending balance	413,876	461,871	540,913
Egypt [Member]
Reserve Quantities [Line Items]
Proved developed reserves	236,256	222,880	221,819	222,651
Proved undeveloped reserves	43,446	48,028	51,464	69,212
Beginning balance	270,908	273,283	291,863
Extensions, discoveries and other additions	60,877	51,135	45,516
Purchase of minerals in-place		5
Revisions of previous estimates	2,776	859	(6,007)
Production	(54,859)	(54,374)	(58,089)
Ending balance	279,702	270,908	273,283
Australia [Member]
Reserve Quantities [Line Items]
Proved developed reserves	136,707	126,948	128,395	148,328
Proved undeveloped reserves	186,534	199,240	213,811	181,214
Beginning balance	326,188	342,206	329,542
Extensions, discoveries and other additions	17,780	4,764	35,772
Purchase of minerals in-place			567
Revisions of previous estimates	(216)	(135)	(49)
Production	(20,511)	(20,647)	(23,626)
Ending balance	323,241	326,188	342,206
North Sea [Member]
Reserve Quantities [Line Items]
Proved developed reserves	122,058	117,457	137,626	163,248
Proved undeveloped reserves	23,301	32,633	31,563	33,493
Beginning balance	150,090	169,189	196,741
Extensions, discoveries and other additions	21,354	2,001	3,325
Purchase of minerals in-place		5,698	3,790
Revisions of previous estimates	(18)	24	(7,258)
Production	(26,067)	(26,822)	(27,409)
Ending balance	145,359	150,090	169,189
Argentina [Member]
Reserve Quantities [Line Items]
Proved developed reserves		66,494	81,695	96,462
Proved undeveloped reserves		23,504	20,106	20,871
Beginning balance	89,998	101,801	117,333
Extensions, discoveries and other additions	5	3,751	1,570
Revisions of previous estimates		35	585
Production	(2,856)	(15,589)	(17,687)
Sale of properties	(87,147)
Ending balance		89,998	101,801
Crude Oil and Condensate [Member]
Reserve Quantities [Line Items]
Proved developed reserves	784,770	794,795	825,811	804,653
Proved undeveloped reserves	289,499	336,690	356,814	356,924
Beginning balance	1,131,485	1,182,625	1,161,577
Extensions, discoveries and other additions	126,387	192,222	147,535
Purchase of minerals in-place	15,240	3,713	18,549
Revisions of previous estimates	3,849	1,533	(16,052)
Production	(117,568)	(126,515)	(128,840)
Sale of properties	(85,124)	(122,093)	(144)
Ending balance	1,074,269	1,131,485	1,182,625
Crude Oil and Condensate [Member] | United States [Member]
Reserve Quantities [Line Items]
Proved developed reserves	444,440	457,981	474,837	428,251
Proved undeveloped reserves	170,125	195,835	203,068	205,763
Beginning balance	653,816	677,905	634,014
Extensions, discoveries and other additions	57,011	133,227	84,656
Purchase of minerals in-place	15,240	85	15,942
Revisions of previous estimates	3,083	1,683	(7,474)
Production	(48,789)	(53,621)	(49,089)
Sale of properties	(65,796)	(105,463)	(144)
Ending balance	614,565	653,816	677,905
Crude Oil and Condensate [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed reserves	75,876	80,526	79,695	81,846
Proved undeveloped reserves	59,923	56,366	70,650	59,746
Beginning balance	136,892	150,345	141,591
Extensions, discoveries and other additions	9,657	10,177	18,935
Purchase of minerals in-place			188
Revisions of previous estimates	(812)	(531)	(4,577)
Production	(6,421)	(6,469)	(5,792)
Sale of properties	(3,517)	(16,630)
Ending balance	135,799	136,892	150,345
Crude Oil and Condensate [Member] | Egypt [Member]
Reserve Quantities [Line Items]
Proved developed reserves	128,712	119,242	106,746	105,840
Proved undeveloped reserves	14,617	16,302	17,288	22,195
Beginning balance	135,544	124,034	128,035
Extensions, discoveries and other additions	38,074	43,738	36,188
Purchase of minerals in-place		5
Revisions of previous estimates	1,801	457	(3,678)
Production	(32,090)	(32,690)	(36,511)
Ending balance	143,329	135,544	124,034
Crude Oil and Condensate [Member] | Australia [Member]
Reserve Quantities [Line Items]
Proved developed reserves	29,996	22,524	29,053	35,725
Proved undeveloped reserves	25,775	36,703	34,808	32,220
Beginning balance	59,227	63,861	67,945
Extensions, discoveries and other additions	4,254	2,539	6,277
Purchase of minerals in-place			276
Revisions of previous estimates	(216)	(118)	(66)
Production	(7,494)	(7,055)	(10,571)
Ending balance	55,771	59,227	63,861
Crude Oil and Condensate [Member] | North Sea [Member]
Reserve Quantities [Line Items]
Proved developed reserves	105,746	100,327	119,635	136,990
Proved undeveloped reserves	19,059	29,253	28,019	32,415
Beginning balance	129,580	147,654	169,405
Extensions, discoveries and other additions	17,386	1,543	346
Purchase of minerals in-place		3,623	2,143
Revisions of previous estimates	(7)	18	(928)
Production	(22,154)	(23,258)	(23,312)
Ending balance	124,805	129,580	147,654
Crude Oil and Condensate [Member] | Argentina [Member]
Reserve Quantities [Line Items]
Proved developed reserves		14,195	15,845	16,001
Proved undeveloped reserves		2,231	2,981	4,585
Beginning balance	16,426	18,826	20,587
Extensions, discoveries and other additions	5	998	1,133
Revisions of previous estimates		24	671
Production	(620)	(3,422)	(3,565)
Sale of properties	(15,811)
Ending balance		16,426	18,826
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved developed reserves	204,628	217,129	183,949	145,438
Proved undeveloped reserves	77,579	74,732	74,403	62,460
Beginning balance	291,861	258,352	207,898
Extensions, discoveries and other additions	50,500	73,245	79,866
Purchase of minerals in-place	2,916	340	470
Revisions of previous estimates	2,691	2,141	(13,626)
Production	(24,589)	(23,595)	(16,256)
Sale of properties	(41,172)	(18,622)
Ending balance	282,207	291,861	258,352
Natural Gas Liquids [Member] | United States [Member]
Reserve Quantities [Line Items]
Proved developed reserves	183,565	184,485	154,508	107,490
Proved undeveloped reserves	69,828	63,538	60,889	52,543
Beginning balance	248,023	215,397	160,033
Extensions, discoveries and other additions	47,516	69,231	71,965
Purchase of minerals in-place	2,916	45	230
Revisions of previous estimates	2,594	1,591	(4,559)
Production	(21,464)	(19,922)	(12,272)
Sale of properties	(26,192)	(18,319)
Ending balance	253,393	248,023	215,397
Natural Gas Liquids [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed reserves	17,947	26,099	21,996	23,256
Proved undeveloped reserves	7,168	9,970	12,258	8,193
Beginning balance	36,069	34,254	31,450
Extensions, discoveries and other additions	1,163	4,014	7,655
Purchase of minerals in-place			9
Revisions of previous estimates	116	546	(2,569)
Production	(2,256)	(2,442)	(2,291)
Sale of properties	(9,977)	(303)
Ending balance	25,115	36,069	34,254
Natural Gas Liquids [Member] | Egypt [Member]
Reserve Quantities [Line Items]
Proved developed reserves	1,346
Proved undeveloped reserves	212
Extensions, discoveries and other additions	1,820
Revisions of previous estimates	(17)
Production	(245)
Ending balance	1,558
Natural Gas Liquids [Member] | North Sea [Member]
Reserve Quantities [Line Items]
Proved developed reserves	1,770	2,435	2,438	8,753
Proved undeveloped reserves	371	215	380	509
Beginning balance	2,650	2,818	9,262
Extensions, discoveries and other additions	1		246
Purchase of minerals in-place		295	231
Revisions of previous estimates	(2)	1	(6,329)
Production	(508)	(464)	(592)
Ending balance	2,141	2,650	2,818
Natural Gas Liquids [Member] | Argentina [Member]
Reserve Quantities [Line Items]
Proved developed reserves		4,110	5,007	5,939
Proved undeveloped reserves		1,009	876	1,215
Beginning balance	5,119	5,883	7,153
Revisions of previous estimates		3	(169)
Production	(116)	(767)	(1,101)
Sale of properties	(5,003)
Ending balance		5,119	5,883
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved developed reserves	3,971,360	4,926,064	5,833,105	6,253,418
Proved undeveloped reserves	2,267,400	2,412,348	2,631,101	3,468,855
Beginning balance	7,338,412	8,464,206	9,722,273
Extensions, discoveries and other additions	817,253	743,212	869,949
Purchase of minerals in-place	21,337	11,535	326,627
Revisions of previous estimates	29,179	173,191	(1,614,206)
Production	(580,043)	(765,437)	(839,403)
Sale of properties	(1,387,378)	(1,288,295)	(1,034)
Ending balance	6,238,760	7,338,412	8,464,206
Natural Gas [Member] | United States [Member]
Reserve Quantities [Line Items]
Proved developed reserves	1,616,504	2,005,966	2,353,587	2,215,973
Proved undeveloped reserves	580,299	667,160	832,320	760,238
Beginning balance	2,673,126	3,185,907	2,976,211
Extensions, discoveries and other additions	203,318	306,721	365,863
Purchase of minerals in-place	21,337	855	313,885
Revisions of previous estimates	35,910	61,247	(156,840)
Production	(215,829)	(285,187)	(312,600)
Sale of properties	(521,059)	(596,417)	(612)
Ending balance	2,196,803	2,673,126	3,185,907
Natural Gas [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed reserves	990,145	1,294,420	1,734,657	2,108,801
Proved undeveloped reserves	527,623	439,037	403,227	1,438,710
Beginning balance	1,733,457	2,137,884	3,547,511
Extensions, discoveries and other additions	383,077	359,493	252,130
Purchase of minerals in-place			2,503
Revisions of previous estimates	(12,626)	109,551	(1,443,989)
Production	(117,816)	(181,593)	(219,849)
Sale of properties	(468,324)	(691,878)	(422)
Ending balance	1,517,768	1,733,457	2,137,884
Natural Gas [Member] | Egypt [Member]
Reserve Quantities [Line Items]
Proved developed reserves	637,187	621,825	690,436	700,866
Proved undeveloped reserves	171,696	190,355	205,055	282,100
Beginning balance	812,180	895,491	982,966
Extensions, discoveries and other additions	125,899	44,382	55,967
Revisions of previous estimates	5,949	2,413	(13,974)
Production	(135,145)	(130,106)	(129,468)
Ending balance	808,883	812,180	895,491
Natural Gas [Member] | Australia [Member]
Reserve Quantities [Line Items]
Proved developed reserves	640,265	626,543	596,052	675,618
Proved undeveloped reserves	964,554	975,224	1,074,018	893,966
Beginning balance	1,601,767	1,670,070	1,569,584
Extensions, discoveries and other additions	81,156	13,351	176,969
Purchase of minerals in-place			1,745
Revisions of previous estimates		(101)	101
Production	(78,104)	(81,553)	(78,329)
Ending balance	1,604,819	1,601,767	1,670,070
Natural Gas [Member] | North Sea [Member]
Reserve Quantities [Line Items]
Proved developed reserves	87,259	88,177	93,319	105,028
Proved undeveloped reserves	23,228	18,988	18,985	3,414
Beginning balance	107,165	112,304	108,442
Extensions, discoveries and other additions	23,803	2,750	16,397
Purchase of minerals in-place		10,680	8,494
Revisions of previous estimates	(54)	32
Production	(20,427)	(18,601)	(21,029)
Ending balance	110,487	107,165	112,304
Natural Gas [Member] | Argentina [Member]
Reserve Quantities [Line Items]
Proved developed reserves		289,133	365,054	447,132
Proved undeveloped reserves		121,584	97,496	90,427
Beginning balance	410,717	462,550	537,559
Extensions, discoveries and other additions		16,515	2,623
Revisions of previous estimates		49	496
Production	(12,722)	(68,397)	(78,128)
Sale of properties	(397,995)
Ending balance		410,717	462,550