Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Freight	CAD 1,547	CAD 1,510	CAD 4,708	CAD 4,464
Non-freight	48	44	133	131
Total revenues	1,595	1,554	4,841	4,595
Operating expenses
Compensation and benefits	256	294	766	907
Fuel	150	138	480	394
Materials	45	39	142	133
Equipment rents	35	43	108	132
Depreciation and amortization	162	155	493	478
Purchased services and other	257	228	812	690
Total operating expenses	905	897	2,801	2,734
Operating income	690	657	2,040	1,861
Less:
Other income and charges	(105)	71	(194)	(119)
Net interest (income) expense	115	116	357	355
Income before income tax expense	680	470	1,877	1,625
Income tax (recovery) expense	170	123	456	410
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	510	347	1,421	1,215
Consolidating Adjustments and Eliminations [Member]
Revenues
Freight	0	0	0	0
Non-freight	(80)	(86)	(249)	(259)
Total revenues	(80)	(86)	(249)	(259)
Operating expenses
Compensation and benefits	3	2	5	5
Fuel	0	0	0	0
Materials	1	3	13	14
Equipment rents	0	0	0	0
Depreciation and amortization	0	0	0	0
Purchased services and other	(84)	(91)	(267)	(278)
Total operating expenses	(80)	(86)	(249)	(259)
Operating income	0	0	0	0
Less:
Other income and charges	0	0	0	0
Net interest (income) expense	0	0	0	0
Income before income tax expense	0	0	0	0
Income tax (recovery) expense	0	0	0	0
Add: Equity in net earnings of subsidiaries	(641)	(512)	(1,798)	(1,532)
Net income	(641)	(512)	(1,798)	(1,532)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Freight	0	0	0	0
Non-freight	0	0	0	0
Total revenues	0	0	0	0
Operating expenses
Compensation and benefits	0	0	0	0
Fuel	0	0	0	0
Materials	0	0	0	0
Equipment rents	0	0	0	0
Depreciation and amortization	0	0	0	0
Purchased services and other	0	0	0	0
Total operating expenses	0	0	0	0
Operating income	0	0	0	0
Less:
Other income and charges	(10)	12	(35)	(61)
Net interest (income) expense	(2)	(9)	(9)	0
Income before income tax expense	12	(3)	44	61
Income tax (recovery) expense	7	9	9	12
Add: Equity in net earnings of subsidiaries	505	359	1,386	1,166
Net income	510	347	1,421	1,215
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Freight	1,092	1,078	3,310	3,182
Non-freight	38	35	104	101
Total revenues	1,130	1,113	3,414	3,283
Operating expenses
Compensation and benefits	149	181	438	563
Fuel	116	111	370	317
Materials	33	30	101	95
Equipment rents	35	48	110	155
Depreciation and amortization	108	102	325	316
Purchased services and other	195	170	613	499
Total operating expenses	636	642	1,957	1,945
Operating income	494	471	1,457	1,338
Less:
Other income and charges	(100)	61	(166)	(89)
Net interest (income) expense	126	131	390	373
Income before income tax expense	468	279	1,233	1,054
Income tax (recovery) expense	99	73	259	254
Add: Equity in net earnings of subsidiaries	136	153	412	366
Net income	505	359	1,386	1,166
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Freight	455	432	1,398	1,282
Non-freight	90	95	278	289
Total revenues	545	527	1,676	1,571
Operating expenses
Compensation and benefits	104	111	323	339
Fuel	34	27	110	77
Materials	11	6	28	24
Equipment rents	0	(5)	(2)	(23)
Depreciation and amortization	54	53	168	162
Purchased services and other	146	149	466	469
Total operating expenses	349	341	1,093	1,048
Operating income	196	186	583	523
Less:
Other income and charges	5	(2)	7	31
Net interest (income) expense	(9)	(6)	(24)	(18)
Income before income tax expense	200	194	600	510
Income tax (recovery) expense	64	41	188	144
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	CAD 136	CAD 153	CAD 412	CAD 366