Segment Information (Income Statement) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenues:
Oil, gas and NGL sales	$ 2,200	$ 1,782	$ 4,060	$ 3,852
Oil, gas and NGL derivatives	416	45	248	665
Marketing and midstream revenues	604	405	1,059	935
Total revenues	3,220	2,232	5,367	5,452
Expenses and other, net:
Lease operating expenses	453	442	877	856
Taxes other than income taxes	120	92	228	193
Marketing and midstream operating costs and expenses	456	280	789	677
Depreciation, depletion and amortization of oil and gas properties	485	426	927	852
Depreciation and amortization of non-oil and gas properties	65	63	129	126
Accretion of asset retirement obligations	23	24	46	50
General and administrative expenses	135	130	265	268
Restructuring costs	6	(8)	1	(8)
Interest expense	85	111	166	197
Interest-rate and other financial instruments	25	81	8	66
Other, net	(11)	(22)	(27)	(26)
Total expenses and other, net	1,842	1,619	3,409	3,251
Earnings from continuing operations before income taxes	1,378	613	1,958	2,201
Income tax expense (benefit):
Current	36	707	(53)	1,006
Deferred	1,158	(446)	1,438	(231)
Total income tax expense	1,194	261	1,385	775
Earnings from continuing operations	184	352	573	1,426
Capital expenditures, before revision of future asset retirement obligations			3,615	3,333
Revision of future asset retirement obligations			16	194
Capital expenditures, continuing operations	1,833	1,919	3,631	3,527
U.S. [Member]
Revenues:
Oil, gas and NGL sales	1,438	1,144	2,650	2,514
Oil, gas and NGL derivatives	416	32	248	657
Marketing and midstream revenues	554	372	977	868
Total revenues	2,408	1,548	3,875	4,039
Expenses and other, net:
Lease operating expenses	224	243	432	467
Taxes other than income taxes	107	83	201	173
Marketing and midstream operating costs and expenses	413	252	721	621
Depreciation, depletion and amortization of oil and gas properties	291	248	551	509
Depreciation and amortization of non-oil and gas properties	59	57	117	113
Accretion of asset retirement obligations	8	12	17	25
General and administrative expenses	94	98	185	206
Restructuring costs	6	(8)	1	(8)
Interest expense	40	55	77	85
Interest-rate and other financial instruments	25	81	8	66
Other, net	(7)	(26)	(21)	(29)
Total expenses and other, net	1,260	1,095	2,289	2,228
Earnings from continuing operations before income taxes	1,148	453	1,586	1,811
Income tax expense (benefit):
Current	35	631	(53)	845
Deferred	1,100	(421)	1,343	(186)
Total income tax expense	1,135	210	1,290	659
Earnings from continuing operations	13	243	296	1,152
Capital expenditures, before revision of future asset retirement obligations			2,749	2,189
Revision of future asset retirement obligations			2	72
Capital expenditures, continuing operations	1,499	1,145	2,751	2,261
Canada [Member]
Revenues:
Oil, gas and NGL sales	762	638	1,410	1,338
Oil, gas and NGL derivatives		13		8
Marketing and midstream revenues	50	33	82	67
Total revenues	812	684	1,492	1,413
Expenses and other, net:
Lease operating expenses	229	199	445	389
Taxes other than income taxes	13	9	27	20
Marketing and midstream operating costs and expenses	43	28	68	56
Depreciation, depletion and amortization of oil and gas properties	194	178	376	343
Depreciation and amortization of non-oil and gas properties	6	6	12	13
Accretion of asset retirement obligations	15	12	29	25
General and administrative expenses	41	32	80	62
Interest expense	45	56	89	112
Other, net	(4)	4	(6)	3
Total expenses and other, net	582	524	1,120	1,023
Earnings from continuing operations before income taxes	230	160	372	390
Income tax expense (benefit):
Current	1	76		161
Deferred	58	(25)	95	(45)
Total income tax expense	59	51	95	116
Earnings from continuing operations	171	109	277	274
Capital expenditures, before revision of future asset retirement obligations			866	1,144
Revision of future asset retirement obligations			14	122
Capital expenditures, continuing operations	$ 334	$ 774	$ 880	$ 1,266