Business Segments (Detail) - CAD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues and other income
Revenues	[1],[2]	$ 34,964	$ 29,125	$ 25,049
Intersegment sales
Investment and other income (note 9)		135	299	2,305
Total revenues and other income		35,099	29,424	27,354
Expenses
Exploration	[3]	19	183	94
Purchases of crude oil and products	[4]	21,541	18,145	15,120
Production and manufacturing	[5]	6,121	5,698	5,224
Selling and general	[5]	908	893	1,129
Federal excise tax		1,667	1,673	1,650
Depreciation and depletion	[3],[6]	1,555	2,172	1,628
Non-service pension and postretirement benefit	[5]	107
Financing (note 13)	[7],[8]	108	78	65
Total expenses		32,026	28,842	24,910
Income (loss) before income taxes		3,073	582	2,444
Income taxes (note 4)
Current	[9]	(14)	(58)	200
Deferred	[9]	773	150	79
Total income tax expense (benefit)	[9],[10]	759	92	279
Net income (loss)		2,314	490	2,165
Cash flows from (used in) operating activities		3,922	2,763	2,015
Capital and exploration expenditures	[11]	1,427	671	1,161
Property, plant and equipment Cost		53,944	52,778	53,515
Accumulated depreciation and depletion		(19,719)	(18,305)	(17,182)
Net property, plant and equipment	[12]	34,225	34,473	36,333
Total assets		41,456	41,601	41,654
Consolidation, Eliminations
Revenues and other income
Intersegment sales		(4,455)	(3,681)	(3,434)
Investment and other income (note 9)
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME		(4,455)	(3,681)	(3,434)
Expenses
Purchases of crude oil and products		(4,449)	(3,675)	(3,429)
Selling and general	[5]	(6)	(6)	(5)
Federal excise tax
Depreciation and depletion	[3],[6]
Non-service pension and postretirement benefit	[5]
Financing (note 13)
Total expenses		(4,455)	(3,681)	(3,434)
Income taxes (note 4)
Cash flows from (used in) operating activities		19		(21)
Total assets		(478)	(435)	(384)
Upstream
Revenues and other income
Revenues	[2]	8,525	7,302	5,492
Intersegment sales		2,634	2,264	2,215
Investment and other income (note 9)		11	16	13
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME		11,170	9,582	7,720
Expenses
Exploration	[3]	19	183	94
Purchases of crude oil and products		5,833	4,526	3,666
Production and manufacturing	[5],[13]	4,305	3,913	3,591
Selling and general	[5]			(5)
Depreciation and depletion	[3],[6]	1,278	1,939	1,396
Financing (note 13)		1	13	(7)
Total expenses		11,436	10,574	8,735
Income (loss) before income taxes		(266)	(992)	(1,015)
Income taxes (note 4)
Current		(184)	484	(491)
Deferred		56	(770)	137
Total income tax expense (benefit)		(128)	(286)	(354)
Net income (loss)		(138)	(706)	(661)
Cash flows from (used in) operating activities		916	1,257	402
Capital and exploration expenditures	[11]	991	416	896
Property, plant and equipment Cost		46,435	45,542	45,850
Accumulated depreciation and depletion		(15,050)	(13,844)	(12,312)
Net property, plant and equipment	[12]	31,385	31,698	33,538
Total assets		34,829	35,044	36,840
Downstream
Revenues and other income
Revenues	[2]	25,200	20,714	18,511
Intersegment sales		1,542	1,155	1,007
Investment and other income (note 9)		95	269	2,278
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME		26,837	22,138	21,796
Expenses
Purchases of crude oil and products		19,326	16,543	14,178
Production and manufacturing	[5],[13]	1,606	1,576	1,428
Selling and general	[5]	773	772	972
Federal excise tax		1,667	1,673	1,650
Depreciation and depletion	[3],[6]	242	202	206
Financing (note 13)		2
Total expenses		23,616	20,766	18,434
Income (loss) before income taxes		3,221	1,372	3,362
Income taxes (note 4)
Current		189	(504)	674
Deferred		666	836	(66)
Total income tax expense (benefit)		855	332	608
Net income (loss)		2,366	1,040	2,754
Cash flows from (used in) operating activities		2,749	1,396	1,574
Capital and exploration expenditures	[11]	383	200	190
Property, plant and equipment Cost		5,900	5,683	6,166
Accumulated depreciation and depletion		(3,763)	(3,594)	(4,037)
Net property, plant and equipment	[12]	2,137	2,089	2,129
Total assets		5,119	4,890	3,958
Chemical
Revenues and other income
Revenues	[2]	1,239	1,109	1,046
Intersegment sales		279	262	212
Investment and other income (note 9)
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME		1,518	1,371	1,258
Expenses
Purchases of crude oil and products		831	751	705
Production and manufacturing	[5]	210	209	205
Selling and general	[5]	87	78	83
Depreciation and depletion	[3],[6]	14	12	10
Total expenses		1,142	1,050	1,003
Income (loss) before income taxes		376	321	255
Income taxes (note 4)
Current		21	(32)	68
Deferred		80	118
Total income tax expense (benefit)		101	86	68
Net income (loss)		275	235	187
Cash flows from (used in) operating activities		354	235	203
Capital and exploration expenditures	[11]	25	17	26
Property, plant and equipment Cost		916	888	872
Accumulated depreciation and depletion		(662)	(644)	(629)
Net property, plant and equipment	[12]	254	244	243
Total assets		438	399	346
Corporate and Other
Revenues and other income
Investment and other income (note 9)		29	14	14
TOTAL OPERATING REVENUES, INTERSEGMENT SALES, INVESTMENT AND OTHER INCOME		29	14	14
Expenses
Selling and general	[5]	54	49	84
Federal excise tax
Depreciation and depletion	[3],[6]	21	19	16
Non-service pension and postretirement benefit	[5]	107
Financing (note 13)		105	65	72
Total expenses		287	133	172
Income (loss) before income taxes		(258)	(119)	(158)
Income taxes (note 4)
Current		(40)	(6)	(51)
Deferred		(29)	(34)	8
Total income tax expense (benefit)		(69)	(40)	(43)
Net income (loss)		(189)	(79)	(115)
Cash flows from (used in) operating activities		(116)	(125)	(143)
Capital and exploration expenditures	[11]	28	38	49
Property, plant and equipment Cost		693	665	627
Accumulated depreciation and depletion		(244)	(223)	(204)
Net property, plant and equipment	[12]	449	442	423
Total assets		$ 1,548	$ 1,703	$ 894

[1] Amounts from related parties included in revenues (note 17). 6,383 4,110 2,342

[2] Includes export sales to the United States of $6,661 million (2017 - $4,392 million, 2016 - $3,612 million). Export sales to the United States were recorded in all operating segments, with the largest effects in the Upstream segment.

[3] The Upstream segment in 2017 includes non-cash impairment charges of $396 million, before tax, associated with the Horn River development and $379 million, before tax, associated with the Mackenzie gas project. The impairment charges are recognized in the lines “Exploration” and “Depreciation and depletion” on the Consolidated statement of income, and the “Accumulated depreciation and depletion” line of the Consolidated balance sheet.

[4] Amounts to related parties included in purchases of crude oil and products (note 17). 4,092 2,687 2,224

[5] As part of the implementation of Accounting Standard Update, Compensation – Retirement Benefits (Topic 715), beginning January 1, 2018, Corporate and other includes all non-service pension and postretirement benefit expense. Prior to 2018, the majority of these costs were allocated to the operating segments. See note 2 for additional details.

[6] The Downstream segment in 2018 includes a non-cash impairment charge of $46 million, before tax, associated with the Government of Ontario’s revocation of its carbon emission cap and trade regulation. The impairment charge is recognized in the “Depreciation and depletion” line on the Consolidated statement of income, and the “Other assets, including intangibles, net” line on the Consolidated balance sheet.

[7] Amounts to related parties included in financing (note 17). 89 60 89

[8] Cash interest payments in 2018 were $88 million (2017 – $58 million, 2016 – $73 million). The weighted average interest rate on short-term borrowings in 2018 was 1.5 percent (2017 – 0.9 percent, 2016 – 0.8 percent). Average effective rate on the long-term borrowings with ExxonMobil in 2018 was 2.0 percent (2017 – 1.3 percent, 2016 – 1.0 percent).

[9] On November 2, 2017 the British Columbia government enacted a 1 percent increase in the provincial tax rate from 11 percent to 12 percent.

[10] Cash outflow from income taxes, plus investment credits earned, was $162 million (2017 - $322 million, 2016 - $172 million).

[11] Capital and exploration expenditures (CAPEX) include exploration expenses, additions to property, plant and equipment, additions to capital leases, additional investments and acquisitions. CAPEX excludes the purchase of carbon emission credits.

[12] Includes property, plant and equipment under construction of $1,553 million (2017 - $1,047 million, 2016 - $2,705 million).

[13] Amounts to related parties included in production and manufacturing, and selling and general expenses (note 17). 566 544 533