Condensed Consolidating Financial Information - Condensed Consolidating Statements of Income (Detail) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Freight									CAD 6,375	CAD 6,060	CAD 6,552
Non-freight									179	172	160
Total revenues	CAD 1,713	CAD 1,595	CAD 1,643	CAD 1,603	CAD 1,637	CAD 1,554	CAD 1,450	CAD 1,591	6,554	6,232	6,712
Operating expenses
Compensation and benefits									1,035	1,189	1,371
Fuel									677	567	708
Materials									190	180	184
Equipment rents									142	173	174
Depreciation and amortization									661	640	595
Purchased Services and Other									1,056	905	1,060
Gain on sale of Delaware & Hudson South									0	0	(68)
Total operating expenses									3,761	3,654	4,024
Operating income	753	690	679	671	717	657	551	653	2,793	2,578	2,688
Less:
Other income and charges									(178)	(45)	335
Net interest expense (income)									473	471	394
Income before income tax expense									2,498	2,152	1,959
Less: Income tax expense (recovery)									93	553	607
Add: Equity in net earnings of subsidiaries									0	0	0
Net income	CAD 984	CAD 510	CAD 480	CAD 431	CAD 384	CAD 347	CAD 328	CAD 540	2,405	1,599	1,352
Consolidating Adjustments and Eliminations [Member]
Revenues
Freight									0	0	0
Non-freight									(333)	(348)	(331)
Total revenues									(333)	(348)	(331)
Operating expenses
Compensation and benefits									7	6	0
Fuel									0	0	0
Materials									15	18	0
Equipment rents									0	0	0
Depreciation and amortization									0	0	0
Purchased Services and Other									(355)	(372)	(331)
Gain on sale of Delaware & Hudson South											0
Total operating expenses									(333)	(348)	(331)
Operating income									0	0	0
Less:
Other income and charges									0	0	0
Net interest expense (income)									0	0	0
Income before income tax expense									0	0	0
Less: Income tax expense (recovery)									0	0	0
Add: Equity in net earnings of subsidiaries									(3,547)	(2,098)	(2,175)
Net income									(3,547)	(2,098)	(2,175)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Freight									0	0	0
Non-freight									0	0	0
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
Gain on sale of Delaware & Hudson South											0
Total operating expenses									0	0	0
Operating income									0	0	0
Less:
Other income and charges									(33)	(40)	84
Net interest expense (income)									(12)	1	(5)
Income before income tax expense									45	39	(79)
Less: Income tax expense (recovery)									7	6	(21)
Add: Equity in net earnings of subsidiaries									2,367	1,566	1,410
Net income									2,405	1,599	1,352
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Freight									4,516	4,332	4,532
Non-freight									140	134	128
Total revenues									4,656	4,466	4,660
Operating expenses
Compensation and benefits									601	749	943
Fuel									522	458	549
Materials									134	130	148
Equipment rents									143	204	181
Depreciation and amortization									400	422	411
Purchased Services and Other									826	673	711
Gain on sale of Delaware & Hudson South											0
Total operating expenses									2,626	2,636	2,943
Operating income									2,030	1,830	1,717
Less:
Other income and charges									(149)	(34)	322
Net interest expense (income)									517	493	447
Income before income tax expense									1,662	1,371	948
Less: Income tax expense (recovery)									475	337	303
Add: Equity in net earnings of subsidiaries									1,180	532	765
Net income									2,367	1,566	1,410
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Freight									1,859	1,728	2,020
Non-freight									372	386	363
Total revenues									2,231	2,114	2,383
Operating expenses
Compensation and benefits									427	434	428
Fuel									155	109	159
Materials									41	32	36
Equipment rents									(1)	(31)	(7)
Depreciation and amortization									261	218	184
Purchased Services and Other									585	604	680
Gain on sale of Delaware & Hudson South											(68)
Total operating expenses									1,468	1,366	1,412
Operating income									763	748	971
Less:
Other income and charges									4	29	(71)
Net interest expense (income)									(32)	(23)	(48)
Income before income tax expense									791	742	1,090
Less: Income tax expense (recovery)									(389)	210	325
Add: Equity in net earnings of subsidiaries									0	0	0
Net income									CAD 1,180	CAD 532	CAD 765