Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Freight	$ 1,625	$ 1,563
Non-freight	37	40
Total revenues	1,662	1,603
Operating expenses
Compensation and benefits	374	300
Fuel	215	170
Materials	55	49
Equipment rents	33	36
Depreciation and amortization	170	166
Purchased services and other	275	278
Total operating expenses	1,122	999
Operating income	540	604
Less:
Other income and charges	51	(28)
Other components of net periodic benefit (recovery) cost	(96)	(67)
Net interest expense (income)	115	120
Income before income tax expense	470	579
Income tax (recovery) expense	122	148
Add: Equity in net earnings of subsidiaries	0	0
Net income	348	431
Consolidating Adjustments and Eliminations [Member]
Revenues
Freight	0	0
Non-freight	(79)	(85)
Total revenues	(79)	(85)
Operating expenses
Compensation and benefits	2	1
Fuel	0	0
Materials	5	6
Equipment rents	0	0
Depreciation and amortization	0	0
Purchased services and other	(86)	(92)
Total operating expenses	(79)	(85)
Operating income	0	0
Less:
Other income and charges	0	0
Other components of net periodic benefit (recovery) cost	0	0
Net interest expense (income)	0	0
Income before income tax expense	0	0
Income tax (recovery) expense	0	0
Add: Equity in net earnings of subsidiaries	(507)	(566)
Net income	(507)	(566)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Freight	0	0
Non-freight	0	0
Total revenues	0	0
Operating expenses
Compensation and benefits	0	0
Fuel	0	0
Materials	0	0
Equipment rents	0	0
Depreciation and amortization	0	0
Purchased services and other	0	0
Total operating expenses	0	0
Operating income	0	0
Less:
Other income and charges	6	(20)
Other components of net periodic benefit (recovery) cost	0	0
Net interest expense (income)	8	2
Income before income tax expense	(14)	18
Income tax (recovery) expense	0	1
Add: Equity in net earnings of subsidiaries	362	414
Net income	348	431
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Freight	1,155	1,089
Non-freight	27	32
Total revenues	1,182	1,121
Operating expenses
Compensation and benefits	257	191
Fuel	168	132
Materials	35	34
Equipment rents	31	36
Depreciation and amortization	104	109
Purchased services and other	218	208
Total operating expenses	813	710
Operating income	369	411
Less:
Other income and charges	48	(7)
Other components of net periodic benefit (recovery) cost	(96)	(67)
Net interest expense (income)	114	125
Income before income tax expense	303	360
Income tax (recovery) expense	86	98
Add: Equity in net earnings of subsidiaries	145	152
Net income	362	414
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Freight	470	474
Non-freight	89	93
Total revenues	559	567
Operating expenses
Compensation and benefits	115	108
Fuel	47	38
Materials	15	9
Equipment rents	2	0
Depreciation and amortization	66	57
Purchased services and other	143	162
Total operating expenses	388	374
Operating income	171	193
Less:
Other income and charges	(3)	(1)
Other components of net periodic benefit (recovery) cost	0	0
Net interest expense (income)	(7)	(7)
Income before income tax expense	181	201
Income tax (recovery) expense	36	49
Add: Equity in net earnings of subsidiaries	0	0
Net income	$ 145	$ 152