Condensed Consolidating Financial Information - Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Total revenues	$ 2,069	$ 1,979	$ 1,977	$ 1,767	$ 2,006	$ 1,898	$ 1,750	$ 1,662	$ 7,792	$ 7,316	$ 6,554
Operating expenses
Compensation and benefits									1,540	1,468	1,309
Fuel									882	918	677
Materials									210	201	190
Equipment rents									137	130	142
Depreciation and amortization									706	696	661
Purchased services and other									1,193	1,072	1,056
Total operating expenses									4,668	4,485	4,035
Operating income	890	869	822	543	874	790	627	540	3,124	2,831	2,519
Less:
Other (income) expense									(89)	174	(178)
Other components of net periodic benefit (recovery) cost									(381)	(384)	(274)
Net interest expense (income)									448	453	473
Income (loss) before income tax (recovery) expense and equity in net earnings of subsidiaries									3,146	2,588	2,498
Income tax expense (recovery)									706	637	93
Add: Equity in net earnings of subsidiaries									0	0	0
Net income	$ 664	$ 618	$ 724	$ 434	$ 545	$ 622	$ 436	$ 348	2,440	1,951	2,405
Freight
Revenues
Total revenues									7,613	7,152	6,375
Non-freight
Revenues
Total revenues									179	164	179
Consolidating Adjustments and Eliminations
Revenues
Total revenues									(524)	(317)	(333)
Operating expenses
Compensation and benefits									8	6	7
Fuel									0	0	0
Materials									15	13	15
Equipment rents									(31)	0	0
Depreciation and amortization									0	0	0
Purchased services and other									(516)	(336)	(355)
Total operating expenses									(524)	(317)	(333)
Operating income									0	0	0
Less:
Other (income) expense									0	0	0
Other components of net periodic benefit (recovery) cost									0	0	0
Net interest expense (income)									0	0	0
Income (loss) before income tax (recovery) expense and equity in net earnings of subsidiaries									0	0	0
Income tax expense (recovery)									0	0	0
Add: Equity in net earnings of subsidiaries									(3,166)	(2,772)	(3,547)
Net income									(3,166)	(2,772)	(3,547)
Consolidating Adjustments and Eliminations | Freight
Revenues
Total revenues									2	0	0
Consolidating Adjustments and Eliminations | Non-freight
Revenues
Total revenues									(526)	(317)	(333)
CPRL (Parent Guarantor) | Reportable Legal Entities
Revenues
Total revenues									0	0	0
Operating expenses
Compensation and benefits									0	0	0
Fuel									0	0	0
Materials									0	0	0
Equipment rents									0	0	0
Depreciation and amortization									0	0	0
Purchased services and other									0	0	0
Total operating expenses									0	0	0
Operating income									0	0	0
Less:
Other (income) expense									(12)	19	(33)
Other components of net periodic benefit (recovery) cost									0	0	0
Net interest expense (income)									(1)	3	(12)
Income (loss) before income tax (recovery) expense and equity in net earnings of subsidiaries									13	(22)	45
Income tax expense (recovery)									3	(4)	7
Add: Equity in net earnings of subsidiaries									2,430	1,969	2,367
Net income									2,440	1,951	2,405
CPRL (Parent Guarantor) | Reportable Legal Entities | Freight
Revenues
Total revenues									0	0	0
CPRL (Parent Guarantor) | Reportable Legal Entities | Non-freight
Revenues
Total revenues									0	0	0
CPRC (Subsidiary Issuer) | Reportable Legal Entities
Revenues
Total revenues									5,662	5,218	4,656
Operating expenses
Compensation and benefits									1,042	996	879
Fuel									695	716	522
Materials									142	139	134
Equipment rents									177	137	143
Depreciation and amortization									423	424	400
Purchased services and other									967	886	826
Total operating expenses									3,446	3,298	2,904
Operating income									2,216	1,920	1,752
Less:
Other (income) expense									(86)	193	(149)
Other components of net periodic benefit (recovery) cost									(388)	(386)	(278)
Net interest expense (income)									474	478	517
Income (loss) before income tax (recovery) expense and equity in net earnings of subsidiaries									2,216	1,635	1,662
Income tax expense (recovery)									522	469	475
Add: Equity in net earnings of subsidiaries									736	803	1,180
Net income									2,430	1,969	2,367
CPRC (Subsidiary Issuer) | Reportable Legal Entities | Freight
Revenues
Total revenues									5,527	5,098	4,516
CPRC (Subsidiary Issuer) | Reportable Legal Entities | Non-freight
Revenues
Total revenues									135	120	140
Non-Guarantor Subsidiaries | Reportable Legal Entities
Revenues
Total revenues									2,654	2,415	2,231
Operating expenses
Compensation and benefits									490	466	423
Fuel									187	202	155
Materials									53	49	41
Equipment rents									(9)	(7)	(1)
Depreciation and amortization									283	272	261
Purchased services and other									742	522	585
Total operating expenses									1,746	1,504	1,464
Operating income									908	911	767
Less:
Other (income) expense									9	(38)	4
Other components of net periodic benefit (recovery) cost									7	2	4
Net interest expense (income)									(25)	(28)	(32)
Income (loss) before income tax (recovery) expense and equity in net earnings of subsidiaries									917	975	791
Income tax expense (recovery)									181	172	(389)
Add: Equity in net earnings of subsidiaries									0	0	0
Net income									736	803	1,180
Non-Guarantor Subsidiaries | Reportable Legal Entities | Freight
Revenues
Total revenues									2,084	2,054	1,859
Non-Guarantor Subsidiaries | Reportable Legal Entities | Non-freight
Revenues
Total revenues									$ 570	$ 361	$ 372