Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Income (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Total revenues	$ 1,767	$ 1,662
Operating expenses
Compensation and benefits	406	374
Fuel	209	215
Materials	57	55
Equipment rents	35	33
Depreciation and amortization	160	170
Purchased services and other	357	275
Total operating expenses	1,224	1,122
Operating income	543	540
Less:
Other (income) expense	(47)	51
Other components of net periodic benefit recovery cost	(97)	(96)
Net interest expense	114	115
Income before income tax expense	573	470
Income tax expense (recovery)	139	122
Equity in net earnings of subsidiaries	0	0
Net income	434	348
Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(102)	(79)
Operating expenses
Compensation and benefits	2	2
Fuel	0	0
Materials	4	5
Equipment rents	0	0
Depreciation and amortization	0	0
Purchased services and other	(108)	(86)
Total operating expenses	(102)	(79)
Operating income	0	0
Less:
Other (income) expense	0	0
Other components of net periodic benefit recovery cost	0	0
Net interest expense	0	0
Income before income tax expense	0	0
Income tax expense (recovery)	0	0
Equity in net earnings of subsidiaries	(552)	(507)
Net income	(552)	(507)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
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) expense	(5)	6
Other components of net periodic benefit recovery cost	0	0
Net interest expense	(1)	8
Income before income tax expense	6	(14)
Income tax expense (recovery)	0	0
Equity in net earnings of subsidiaries	428	362
Net income	434	348
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	1,273	1,182
Operating expenses
Compensation and benefits	274	257
Fuel	165	168
Materials	38	35
Equipment rents	33	31
Depreciation and amortization	96	104
Purchased services and other	278	218
Total operating expenses	884	813
Operating income	389	369
Less:
Other (income) expense	(43)	48
Other components of net periodic benefit recovery cost	(98)	(96)
Net interest expense	122	114
Income before income tax expense	408	303
Income tax expense (recovery)	104	86
Equity in net earnings of subsidiaries	124	145
Net income	428	362
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	596	559
Operating expenses
Compensation and benefits	130	115
Fuel	44	47
Materials	15	15
Equipment rents	2	2
Depreciation and amortization	64	66
Purchased services and other	187	143
Total operating expenses	442	388
Operating income	154	171
Less:
Other (income) expense	1	(3)
Other components of net periodic benefit recovery cost	1	0
Net interest expense	(7)	(7)
Income before income tax expense	159	181
Income tax expense (recovery)	35	36
Equity in net earnings of subsidiaries	0	0
Net income	124	145
Freight [Member]
Revenues
Total revenues	1,726	1,625
Freight [Member] | Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	0	0
Freight [Member] | CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	0	0
Freight [Member] | CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	1,244	1,155
Freight [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	482	470
Non-Freight [Member]
Revenues
Total revenues	41	37
Non-Freight [Member] | Consolidating Adjustments and Eliminations [Member]
Revenues
Total revenues	(102)	(79)
Non-Freight [Member] | CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	0	0
Non-Freight [Member] | CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	29	27
Non-Freight [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Total revenues	$ 114	$ 89