Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Total revenues	$ 1,977	$ 1,750	$ 3,744	$ 3,412
Operating expenses
Compensation and benefits	383	351	789	725
Fuel	236	230	445	445
Materials	54	53	111	108
Equipment rents	34	33	69	66
Depreciation and amortization	183	172	343	342
Purchased services and other	265	284	622	559
Total operating expenses	1,155	1,123	2,379	2,245
Operating income	822	627	1,365	1,167
Less:
Other expense (income)	(40)	52	(87)	103
Other components of net periodic benefit recovery cost	(98)	(95)	(195)	(191)
Net interest (income) expense	112	112	226	227
Income before income tax expense and equity in net earnings of subsidiaries	848	558	1,421	1,028
Income tax expense (recovery)	124	122	263	244
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	724	436	1,158	784
Freight
Revenues
Total revenues	1,931	1,709	3,657	3,334
Non-freight
Revenues
Total revenues	46	41	87	78
Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(103)	(80)	(205)	(159)
Operating expenses
Compensation and benefits	1	0	3	2
Fuel	0	0	0	0
Materials	4	3	8	8
Equipment rents	0	0	0	0
Depreciation and amortization	0	0	0	0
Purchased services and other	(108)	(83)	(216)	(169)
Total operating expenses	(103)	(80)	(205)	(159)
Operating income	0	0	0	0
Less:
Other expense (income)	0	0	0	0
Other components of net periodic benefit recovery cost	0	0	0	0
Net interest (income) expense	0	0	0	0
Income before income tax expense and equity in net earnings of subsidiaries	0	0	0	0
Income tax expense (recovery)	0	0	0	0
Add: Equity in net earnings of subsidiaries	(978)	(645)	(1,530)	(1,152)
Net income	(978)	(645)	(1,530)	(1,152)
Consolidating Adjustments and Eliminations [Member] | Freight
Revenues
Total revenues	0	0	0	0
Consolidating Adjustments and Eliminations [Member] | Non-freight
Revenues
Total revenues	(103)	(80)	(205)	(159)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
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 expense (income)	(5)	5	(10)	11
Other components of net periodic benefit recovery cost	0	0	0	0
Net interest (income) expense	(1)	(2)	(2)	6
Income before income tax expense and equity in net earnings of subsidiaries	6	(3)	12	(17)
Income tax expense (recovery)	2	(1)	2	(1)
Add: Equity in net earnings of subsidiaries	720	438	1,148	800
Net income	724	436	1,158	784
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member] | Freight
Revenues
Total revenues	0	0	0	0
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member] | Non-freight
Revenues
Total revenues	0	0	0	0
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	1,437	1,227	2,710	2,409
Operating expenses
Compensation and benefits	257	237	531	494
Fuel	189	178	354	346
Materials	37	38	75	73
Equipment rents	47	30	80	61
Depreciation and amortization	110	105	206	209
Purchased services and other	240	205	518	423
Total operating expenses	880	793	1,764	1,606
Operating income	557	434	946	803
Less:
Other expense (income)	(38)	79	(81)	127
Other components of net periodic benefit recovery cost	(100)	(96)	(198)	(192)
Net interest (income) expense	120	121	242	235
Income before income tax expense and equity in net earnings of subsidiaries	575	330	983	633
Income tax expense (recovery)	113	99	217	185
Add: Equity in net earnings of subsidiaries	258	207	382	352
Net income	720	438	1,148	800
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Freight
Revenues
Total revenues	1,403	1,196	2,647	2,351
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Non-freight
Revenues
Total revenues	34	31	63	58
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	643	603	1,239	1,162
Operating expenses
Compensation and benefits	125	114	255	229
Fuel	47	52	91	99
Materials	13	12	28	27
Equipment rents	(13)	3	(11)	5
Depreciation and amortization	73	67	137	133
Purchased services and other	133	162	320	305
Total operating expenses	378	410	820	798
Operating income	265	193	419	364
Less:
Other expense (income)	3	(32)	4	(35)
Other components of net periodic benefit recovery cost	2	1	3	1
Net interest (income) expense	(7)	(7)	(14)	(14)
Income before income tax expense and equity in net earnings of subsidiaries	267	231	426	412
Income tax expense (recovery)	9	24	44	60
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	258	207	382	352
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Freight
Revenues
Total revenues	528	513	1,010	983
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Non-freight
Revenues
Total revenues	$ 115	$ 90	$ 229	$ 179