Business Segments (Detail) (CAD) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
REVENUES AND OTHER INCOME
Operating revenues	7,452	[1],[2]	7,761	[1],[2]	14,946	[1],[2]	14,613	[1],[2]
Investment and other income	63		13		102		32
TOTAL REVENUES AND OTHER INCOME	7,515		7,774		15,048		14,645
EXPENSES
Exploration	18		22		46		59
Purchases of crude oil and products	4,645	[3]	4,966	[3]	9,031	[3]	8,946	[3]
Production and manufacturing	1,247	[4]	1,058	[4]	2,224	[4]	2,037	[4]
Selling and general	247		253		531		574
Federal excise tax	340	[1]	325	[1]	656	[1]	640	[1]
Depreciation and depletion	178		190		368		378
Financing costs			1				1
TOTAL EXPENSES	6,675		6,815		12,856		12,635
INCOME BEFORE INCOME TAXES	840		959		2,192		2,010
INCOME TAXES	205		233		542		503
Net income	635		726		1,650		1,507
Export sales to the United States	1,133		1,094		2,038		2,094
Cash flows from (used in) operating activities	1,317		656		2,364		1,615
CAPEX	1,308	[5]	925	[5]	2,481	[5]	1,784	[5]
Total assets as at June 30	27,241		22,966		27,241		22,966		25,429
Upstream
REVENUES AND OTHER INCOME
Operating revenues	1,073		1,400		2,468		2,574
Intersegment sales	948		1,140		2,042		2,297
Investment and other income	38		3		41		11
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME	2,059		2,543		4,551		4,882
EXPENSES
Exploration	18		22		46		59
Purchases of crude oil and products	740		963		1,761		1,824
Production and manufacturing	701		596		1,292		1,195
Selling and general			2		2		3
Depreciation and depletion	119		132		248		265
TOTAL EXPENSES	1,578		1,715		3,349		3,346
INCOME BEFORE INCOME TAXES	481		828		1,202		1,536
INCOME TAXES	121		204		300		384
Net income	360		624		902		1,152
Export sales to the United States	386		559		849		1,108
Cash flows from (used in) operating activities	599		823		1,486		1,540
CAPEX	1,272	[5]	884	[5]	2,417	[5]	1,702	[5]
Total assets as at June 30	19,146		15,184		19,146		15,184
Downstream
REVENUES AND OTHER INCOME
Operating revenues	6,032		6,021		11,787		11,368
Intersegment sales	594		728		1,388		1,439
Investment and other income	22		9		55		18
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME	6,648		6,758		13,230		12,825
EXPENSES
Purchases of crude oil and products	5,234		5,647		10,255		10,416
Production and manufacturing	499		415		840		752
Selling and general	222		237		463		460
Federal excise tax	340		325		656		640
Depreciation and depletion	52		52		108		102
Financing costs			1
TOTAL EXPENSES	6,347		6,677		12,322		12,370
INCOME BEFORE INCOME TAXES	301		81		908		455
INCOME TAXES	69		17		221		115
Net income	232		64		687		340
Export sales to the United States	517		307		748		558
Cash flows from (used in) operating activities	591		(252)		778		19
CAPEX	30	[5]	36	[5]	53	[5]	72	[5]
Total assets as at June 30	6,633		7,044		6,633		7,044
Chemical
REVENUES AND OTHER INCOME
Operating revenues	347		340		691		671
Intersegment sales	69		105		151		194
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME	416		445		842		865
EXPENSES
Purchases of crude oil and products	282		329		596		636
Production and manufacturing	47		47		92		90
Selling and general	16		16		33		32
Depreciation and depletion	4		4		7		7
TOTAL EXPENSES	349		396		728		765
INCOME BEFORE INCOME TAXES	67		49		114		100
INCOME TAXES	18		13		30		26
Net income	49		36		84		74
Export sales to the United States	230		228		441		428
Cash flows from (used in) operating activities	99		77		46		82
CAPEX	1	[5]	1	[5]	2	[5]	3	[5]
Total assets as at June 30	368		416		368		416
Corporate and Other
REVENUES AND OTHER INCOME
Investment and other income	3		1		6		3
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME	3		1		6		3
EXPENSES
Selling and general	9		(2)		33		79
Depreciation and depletion	3		2		5		4
Financing costs							1
TOTAL EXPENSES	12				38		84
INCOME BEFORE INCOME TAXES	(9)		1		(32)		(81)
INCOME TAXES	(3)		(1)		(9)		(22)
Net income	(6)		2		(23)		(59)
Cash flows from (used in) operating activities	28		8		54		(26)
CAPEX	5	[5]	4	[5]	9	[5]	7	[5]
Total assets as at June 30	1,221		640		1,221		640
Eliminations
REVENUES AND OTHER INCOME
Intersegment sales	(1,611)		(1,973)		(3,581)		(3,930)
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME	(1,611)		(1,973)		(3,581)		(3,930)
EXPENSES
Purchases of crude oil and products	(1,611)		(1,973)		(3,581)		(3,930)
TOTAL EXPENSES	(1,611)		(1,973)		(3,581)		(3,930)
Total assets as at June 30	(127)		(318)		(127)		(318)

[1] Federal excise tax included in operating revenues 340 325 656 640

[2] Amounts from related parties included in operating revenues 938 638 1,645 1,120

[3] Amounts to related parties included in purchases of crude oil and products 1,022 766 1,555 1,881

[4] Amounts to related parties included in production and manufacturing expenses 71 48 105 101

[5] Capital and exploration expenditures (CAPEX) include exploration expenses, additions to property, plant, equipment and additions to capital leases.