Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Total revenues	$ 1,979	$ 1,898	$ 5,723	$ 5,310
Operating expenses
Compensation and benefits	355	365	1,144	1,090
Fuel	210	226	655	671
Materials	50	47	161	155
Equipment rents	33	33	102	99
Depreciation and amortization	185	174	528	516
Purchased services and other	277	263	899	822
Total operating expenses	1,110	1,108	3,489	3,353
Operating income	869	790	2,234	1,957
Less:
Other expense (income)	29	(47)	(58)	56
Other components of net periodic benefit recovery cost	(99)	(96)	(294)	(287)
Net interest (income) expense	110	112	336	339
(Loss) income before income tax expense and equity in net earnings of subsidiaries	829	821	2,250	1,849
Income tax expense (recovery)	211	199	474	443
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	618	622	1,776	1,406
Freight
Revenues
Total revenues	1,932	1,854	5,589	5,188
Non-freight
Revenues
Total revenues	47	44	134	122
Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(103)	(79)	(308)	(238)
Operating expenses
Compensation and benefits	3	2	6	4
Fuel	0	0	0	0
Materials	3	3	11	11
Equipment rents	0	0	0	0
Depreciation and amortization	0	0	0	0
Purchased services and other	(109)	(84)	(325)	(253)
Total operating expenses	(103)	(79)	(308)	(238)
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
(Loss) 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	(808)	(815)	(2,338)	(1,967)
Net income	(808)	(815)	(2,338)	(1,967)
Consolidating Adjustments and Eliminations [Member] | Freight
Revenues
Total revenues	0	0	0	0
Consolidating Adjustments and Eliminations [Member] | Non-freight
Revenues
Total revenues	(103)	(79)	(308)	(238)
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)	3	(4)	(7)	7
Other components of net periodic benefit recovery cost	0	0	0	0
Net interest (income) expense	0	(2)	(2)	4
(Loss) income before income tax expense and equity in net earnings of subsidiaries	(3)	6	9	(11)
Income tax expense (recovery)	1	(1)	3	(2)
Add: Equity in net earnings of subsidiaries	622	615	1,770	1,415
Net income	618	622	1,776	1,406
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	1,416	1,347	4,126	3,756
Operating expenses
Compensation and benefits	238	246	769	740
Fuel	164	177	518	523
Materials	35	33	110	106
Equipment rents	36	27	116	88
Depreciation and amortization	112	105	318	314
Purchased services and other	194	224	712	647
Total operating expenses	779	812	2,543	2,418
Operating income	637	535	1,583	1,338
Less:
Other expense (income)	27	(46)	(54)	81
Other components of net periodic benefit recovery cost	(100)	(97)	(298)	(289)
Net interest (income) expense	118	121	360	356
(Loss) income before income tax expense and equity in net earnings of subsidiaries	592	557	1,575	1,190
Income tax expense (recovery)	156	142	373	327
Add: Equity in net earnings of subsidiaries	186	200	568	552
Net income	622	615	1,770	1,415
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Freight
Revenues
Total revenues	1,381	1,316	4,028	3,667
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member] | Non-freight
Revenues
Total revenues	35	31	98	89
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	666	630	1,905	1,792
Operating expenses
Compensation and benefits	114	117	369	346
Fuel	46	49	137	148
Materials	12	11	40	38
Equipment rents	(3)	6	(14)	11
Depreciation and amortization	73	69	210	202
Purchased services and other	192	123	512	428
Total operating expenses	434	375	1,254	1,173
Operating income	232	255	651	619
Less:
Other expense (income)	(1)	3	3	(32)
Other components of net periodic benefit recovery cost	1	1	4	2
Net interest (income) expense	(8)	(7)	(22)	(21)
(Loss) income before income tax expense and equity in net earnings of subsidiaries	240	258	666	670
Income tax expense (recovery)	54	58	98	118
Add: Equity in net earnings of subsidiaries	0	0	0	0
Net income	186	200	568	552
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Freight
Revenues
Total revenues	551	538	1,561	1,521
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Non-freight
Revenues
Total revenues	$ 115	$ 92	$ 344	$ 271