Condensed Consolidating Financial Information - Condensed Consolidating Statements of Income (Detail) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 2,006	$ 1,898	$ 1,750	$ 1,662	$ 1,713	$ 1,595	$ 1,643	$ 1,603	$ 7,316	$ 6,554	$ 6,232
Operating expenses
Compensation and benefits									1,468	1,309	1,356
Fuel									918	677	567
Materials									201	190	180
Equipment rents									130	142	173
Depreciation and amortization									696	661	640
Purchased services and other									1,072	1,056	905
Total operating expenses									4,485	4,035	3,821
Operating income	874	790	627	540	682	622	611	604	2,831	2,519	2,411
Less:
Other expense (income)									174	(178)	(45)
Other components of net periodic benefit (recovery) cost									(384)	(274)	(167)
Net interest expense (income)									453	473	471
(Loss) income before income tax (recovery) expense and equity in net earnings of subsidiaries									2,588	2,498	2,152
Less: Income tax (recovery) expense									637	93	553
Add: Equity in net earnings of subsidiaries									0	0	0
Net income	$ 545	$ 622	$ 436	$ 348	$ 984	$ 510	$ 480	$ 431	1,951	2,405	1,599
Freight [Member]
Revenues
Revenues									7,152	6,375	6,060
Non-freight [Member]
Revenues
Revenues									164	179	172
Consolidating Adjustments and Eliminations [Member]
Revenues
Revenues									(317)	(333)	(348)
Operating expenses
Compensation and benefits									6	7	6
Fuel									0	0	0
Materials									13	15	18
Equipment rents									0	0	0
Depreciation and amortization									0	0	0
Purchased services and other									(336)	(355)	(372)
Total operating expenses									(317)	(333)	(348)
Operating income									0	0	0
Less:
Other expense (income)									0	0	0
Other components of net periodic benefit (recovery) cost									0	0	0
Net interest expense (income)									0	0	0
(Loss) income before income tax (recovery) expense and equity in net earnings of subsidiaries									0	0	0
Less: Income tax (recovery) expense									0	0	0
Add: Equity in net earnings of subsidiaries									(2,772)	(3,547)	(2,098)
Net income									(2,772)	(3,547)	(2,098)
Consolidating Adjustments and Eliminations [Member] | Freight [Member]
Revenues
Revenues									0	0	0
Consolidating Adjustments and Eliminations [Member] | Non-freight [Member]
Revenues
Revenues									(317)	(333)	(348)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
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 expense (income)									19	(33)	(40)
Other components of net periodic benefit (recovery) cost									0	0	0
Net interest expense (income)									3	(12)	1
(Loss) income before income tax (recovery) expense and equity in net earnings of subsidiaries									(22)	45	39
Less: Income tax (recovery) expense									(4)	7	6
Add: Equity in net earnings of subsidiaries									1,969	2,367	1,566
Net income									1,951	2,405	1,599
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member] | Freight [Member]
Revenues
Revenues									0	0	0
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member] | Non-freight [Member]
Revenues
Revenues									0	0	0
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Revenues									5,218	4,656	4,466
Operating expenses
Compensation and benefits									996	879	923
Fuel									716	522	458
Materials									139	134	130
Equipment rents									137	143	204
Depreciation and amortization									424	400	422
Purchased services and other									886	826	673
Total operating expenses									3,298	2,904	2,810
Operating income									1,920	1,752	1,656
Less:
Other expense (income)									193	(149)	(34)
Other components of net periodic benefit (recovery) cost									(386)	(278)	(174)
Net interest expense (income)									478	517	493
(Loss) income before income tax (recovery) expense and equity in net earnings of subsidiaries									1,635	1,662	1,371
Less: Income tax (recovery) expense									469	475	337
Add: Equity in net earnings of subsidiaries									803	1,180	532
Net income									1,969	2,367	1,566
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Freight [Member]
Revenues
Revenues									5,098	4,516	4,332
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Non-freight [Member]
Revenues
Revenues									120	140	134
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Revenues									2,415	2,231	2,114
Operating expenses
Compensation and benefits									466	423	427
Fuel									202	155	109
Materials									49	41	32
Equipment rents									(7)	(1)	(31)
Depreciation and amortization									272	261	218
Purchased services and other									522	585	604
Total operating expenses									1,504	1,464	1,359
Operating income									911	767	755
Less:
Other expense (income)									(38)	4	29
Other components of net periodic benefit (recovery) cost									2	4	7
Net interest expense (income)									(28)	(32)	(23)
(Loss) income before income tax (recovery) expense and equity in net earnings of subsidiaries									975	791	742
Less: Income tax (recovery) expense									172	(389)	210
Add: Equity in net earnings of subsidiaries									0	0	0
Net income									803	1,180	532
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Freight [Member]
Revenues
Revenues									2,054	1,859	1,728
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Non-freight [Member]
Revenues
Revenues									$ 361	$ 372	$ 386