Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 352		$ 61
Accounts receivable, net	744		815
Accounts receivable, inter-company	0		0
Short-term advances to affiliates	0		0
Materials and supplies	182		173
Other current assets	98		68
Total current assets	1,376		1,117
Long-term advances to affiliates	0		0
Investments	201		203
Investments in subsidiaries	0		0
Properties	18,312	$ 18,406	18,418
Goodwill and intangible assets	198		202
Pension asset	1,352		1,243
Other assets	471	470	71
Deferred income taxes	0		0
Total assets	21,910		21,254
Current liabilities
Accounts payable and accrued liabilities	1,312	1,507	1,449
Accounts payable, inter-company	0		0
Short-term advances from affiliates	0		0
Long-term debt maturing within one year	496		506
Total current liabilities	1,808		1,955
Pension and other benefit liabilities	714		718
Long-term advances from affiliates	0		0
Other long-term liabilities	598	574	237
Long-term debt	8,427		8,190
Deferred income taxes	3,549	3,515	3,518
Total liabilities	15,096		14,618
Shareholders’ equity
Share capital	1,997		2,002
Additional paid-in capital	46		42
Accumulated other comprehensive (loss) income	(2,027)		(2,043)	$ (1,705)	$ (1,741)
Retained earnings	6,798	6,630	6,635
Total shareholders' equity	6,814	$ 6,631	6,636	$ 6,434	$ 6,437
Total liabilities and shareholders’ equity	21,910		21,254
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Accounts receivable, inter-company	(504)		(516)
Short-term advances to affiliates	(5,886)		(6,253)
Materials and supplies	0		0
Other current assets	0		0
Total current assets	(6,390)		(6,769)
Long-term advances to affiliates	(1,186)		(1,188)
Investments	0		0
Investments in subsidiaries	(23,227)		(23,446)
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	(6)		(6)
Total assets	(30,809)		(31,409)
Current liabilities
Accounts payable and accrued liabilities	0		0
Accounts payable, inter-company	(504)		(516)
Short-term advances from affiliates	(5,886)		(6,253)
Long-term debt maturing within one year	0		0
Total current liabilities	(6,390)		(6,769)
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	(1,186)		(1,188)
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	(6)		(6)
Total liabilities	(7,582)		(7,963)
Shareholders’ equity
Share capital	(6,483)		(6,484)
Additional paid-in capital	(1,757)		(1,748)
Accumulated other comprehensive (loss) income	1,291		1,204
Retained earnings	(16,278)		(16,418)
Total shareholders' equity	(23,227)		(23,446)
Total liabilities and shareholders’ equity	(30,809)		(31,409)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Accounts receivable, inter-company	131		125
Short-term advances to affiliates	0		0
Materials and supplies	0		0
Other current assets	0		0
Total current assets	131		125
Long-term advances to affiliates	1,090		1,090
Investments	0		0
Investments in subsidiaries	11,195		11,443
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	6		6
Total assets	12,422		12,664
Current liabilities
Accounts payable and accrued liabilities	93		115
Accounts payable, inter-company	3		4
Short-term advances from affiliates	5,512		5,909
Long-term debt maturing within one year	0		0
Total current liabilities	5,608		6,028
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	0		0
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	0		0
Total liabilities	5,608		6,028
Shareholders’ equity
Share capital	1,997		2,002
Additional paid-in capital	46		42
Accumulated other comprehensive (loss) income	(2,027)		(2,043)
Retained earnings	6,798		6,635
Total shareholders' equity	6,814		6,636
Total liabilities and shareholders’ equity	12,422		12,664
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	226		42
Accounts receivable, net	562		629
Accounts receivable, inter-company	166		167
Short-term advances to affiliates	1,205		1,602
Materials and supplies	145		136
Other current assets	78		39
Total current assets	2,382		2,615
Long-term advances to affiliates	5		5
Investments	26		24
Investments in subsidiaries	12,032		12,003
Properties	9,592		9,579
Goodwill and intangible assets	0		0
Pension asset	1,352		1,243
Other assets	141		57
Deferred income taxes	0		0
Total assets	25,530		25,526
Current liabilities
Accounts payable and accrued liabilities	864		1,017
Accounts payable, inter-company	335		344
Short-term advances from affiliates	370		341
Long-term debt maturing within one year	496		506
Total current liabilities	2,065		2,208
Pension and other benefit liabilities	637		639
Long-term advances from affiliates	1,180		1,182
Other long-term liabilities	229		120
Long-term debt	8,373		8,135
Deferred income taxes	1,851		1,799
Total liabilities	14,335		14,083
Shareholders’ equity
Share capital	537		538
Additional paid-in capital	1,663		1,656
Accumulated other comprehensive (loss) income	(2,027)		(2,043)
Retained earnings	11,022		11,292
Total shareholders' equity	11,195		11,443
Total liabilities and shareholders’ equity	25,530		25,526
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	126		19
Accounts receivable, net	182		186
Accounts receivable, inter-company	207		224
Short-term advances to affiliates	4,681		4,651
Materials and supplies	37		37
Other current assets	20		29
Total current assets	5,253		5,146
Long-term advances to affiliates	91		93
Investments	175		179
Investments in subsidiaries	0		0
Properties	8,720		8,839
Goodwill and intangible assets	198		202
Pension asset	0		0
Other assets	330		14
Deferred income taxes	0		0
Total assets	14,767		14,473
Current liabilities
Accounts payable and accrued liabilities	355		317
Accounts payable, inter-company	166		168
Short-term advances from affiliates	4		3
Long-term debt maturing within one year	0		0
Total current liabilities	525		488
Pension and other benefit liabilities	77		79
Long-term advances from affiliates	6		6
Other long-term liabilities	369		117
Long-term debt	54		55
Deferred income taxes	1,704		1,725
Total liabilities	2,735		2,470
Shareholders’ equity
Share capital	5,946		5,946
Additional paid-in capital	94		92
Accumulated other comprehensive (loss) income	736		839
Retained earnings	5,256		5,126
Total shareholders' equity	12,032		12,003
Total liabilities and shareholders’ equity	$ 14,767		$ 14,473