Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues
Total revenues	$ 1,898	$ 1,595	$ 5,310	$ 4,841
Operating expenses
Compensation and benefits	365	324	1,090	969
Fuel	226	150	671	480
Materials	47	45	155	142
Equipment Rents	33	35	99	108
Depreciation and amortization	174	162	516	493
Purchased services and other	263	257	822	812
Total operating expenses	1,108	973	3,353	3,004
Operating income	790	622	1,957	1,837
Less:
Other (income) expense	(47)	(105)	56	(194)
Other components of net periodic benefit recovery cost	(96)	(68)	(287)	(203)
Net interest expense (income)	112	115	339	357
Income before income tax expense	821	680	1,849	1,877
Income tax expense (recovery)	199	170	443	456
Equity in net earnings of subsidiaries	0	0	0	0
Net income	622	510	1,406	1,421
Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(79)	(80)	(238)	(249)
Operating expenses
Compensation and benefits	2	3	4	5
Fuel	0	0	0	0
Materials	3	1	11	13
Equipment Rents	0	0	0	0
Depreciation and amortization	0	0	0	0
Purchased services and other	(84)	(84)	(253)	(267)
Total operating expenses	(79)	(80)	(238)	(249)
Operating income	0	0	0	0
Less:
Other (income) expense	0	0	0	0
Other components of net periodic benefit recovery cost	0	0	0	0
Net interest expense (income)	0	0	0	0
Income before income tax expense	0	0	0	0
Income tax expense (recovery)	0	0	0	0
Equity in net earnings of subsidiaries	(815)	(641)	(1,967)	(1,798)
Net income	(815)	(641)	(1,967)	(1,798)
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 (income) expense	(4)	(10)	7	(35)
Other components of net periodic benefit recovery cost	0	0	0	0
Net interest expense (income)	(2)	(2)	4	(9)
Income before income tax expense	6	12	(11)	44
Income tax expense (recovery)	(1)	7	(2)	9
Equity in net earnings of subsidiaries	615	505	1,415	1,386
Net income	622	510	1,406	1,421
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	1,347	1,130	3,756	3,414
Operating expenses
Compensation and benefits	246	218	740	644
Fuel	177	116	523	370
Materials	33	33	106	101
Equipment Rents	27	35	88	110
Depreciation and amortization	105	108	314	325
Purchased services and other	224	195	647	613
Total operating expenses	812	705	2,418	2,163
Operating income	535	425	1,338	1,251
Less:
Other (income) expense	(46)	(100)	81	(166)
Other components of net periodic benefit recovery cost	(97)	(69)	(289)	(206)
Net interest expense (income)	121	126	356	390
Income before income tax expense	557	468	1,190	1,233
Income tax expense (recovery)	142	99	327	259
Equity in net earnings of subsidiaries	200	136	552	412
Net income	615	505	1,415	1,386
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	630	545	1,792	1,676
Operating expenses
Compensation and benefits	117	103	346	320
Fuel	49	34	148	110
Materials	11	11	38	28
Equipment Rents	6	0	11	(2)
Depreciation and amortization	69	54	202	168
Purchased services and other	123	146	428	466
Total operating expenses	375	348	1,173	1,090
Operating income	255	197	619	586
Less:
Other (income) expense	3	5	(32)	7
Other components of net periodic benefit recovery cost	1	1	2	3
Net interest expense (income)	(7)	(9)	(21)	(24)
Income before income tax expense	258	200	670	600
Income tax expense (recovery)	58	64	118	188
Equity in net earnings of subsidiaries	0	0	0	0
Net income	200	136	552	412
Cargo and Freight [Member]
Revenues
Total revenues	1,854	1,547	5,188	4,708
Cargo and Freight [Member] | Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	0	0	0	0
Cargo and Freight [Member] | CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	0	0	0	0
Cargo and Freight [Member] | CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	1,316	1,092	3,667	3,310
Cargo and Freight [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	538	455	1,521	1,398
Non-Freight [Member]
Revenues
Total revenues	44	48	122	133
Non-Freight [Member] | Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(79)	(80)	(238)	(249)
Non-Freight [Member] | CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	0	0	0	0
Non-Freight [Member] | CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	31	38	89	104
Non-Freight [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	$ 92	$ 90	$ 271	$ 278