Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Details) - CAD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 133		$ 61
Accounts receivable, net	805		815
Accounts receivable, intercompany	0		0
Short-term advances to affiliates	0		0
Materials and supplies	182		173
Other current assets	90		68
Total current assets	1,210		1,117
Long-term advances to affiliates	0		0
Investments	341		203
Investments in subsidiaries	0		0
Properties	19,156	$ 18,406	18,418
Goodwill and intangible assets	206		202	$ 187
Pension asset	1,003		1,243
Other assets	451	470	71
Deferred income taxes	0		0
Total assets	22,367		21,254
Current liabilities
Accounts payable and accrued liabilities	1,693	1,507	1,449
Accounts payable, intercompany	0		0
Short-term advances from affiliates	0		0
Long-term debt maturing within one year	599		506
Total current liabilities	2,292		1,955
Pension and other benefit liabilities	785		718
Long-term advances from affiliates	0		0
Other long-term liabilities	562	574	237
Long-term debt	8,158		8,190
Deferred income taxes	3,501	3,515	3,518
Total liabilities	15,298		14,618
Shareholders’ equity
Share capital	1,993		2,002
Additional paid-in capital	48		42
Accumulated other comprehensive (loss) income	(2,522)		(2,043)	(1,741)
Retained earnings	7,550		6,635
Total shareholders' equity	7,069	$ 6,631	6,636	$ 6,437	$ 4,626
Total liabilities and shareholders’ equity	22,367		21,254
Consolidating Adjustments and Eliminations
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Accounts receivable, intercompany	(726)		(516)
Short-term advances to affiliates	(5,087)		(6,253)
Materials and supplies	0		0
Other current assets	0		0
Total current assets	(5,813)		(6,769)
Long-term advances to affiliates	(1,181)		(1,188)
Investments	0		0
Investments in subsidiaries	(21,687)		(23,446)
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	(4)		(6)
Total assets	(28,685)		(31,409)
Current liabilities
Accounts payable and accrued liabilities	0		0
Accounts payable, intercompany	(726)		(516)
Short-term advances from affiliates	(5,087)		(6,253)
Long-term debt maturing within one year	0		0
Total current liabilities	(5,813)		(6,769)
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	(1,181)		(1,188)
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	(4)		(6)
Total liabilities	(6,998)		(7,963)
Shareholders’ equity
Share capital	(5,148)		(6,484)
Additional paid-in capital	(671)		(1,748)
Accumulated other comprehensive (loss) income	1,941		1,204
Retained earnings	(17,809)		(16,418)
Total shareholders' equity	(21,687)		(23,446)
Total liabilities and shareholders’ equity	(28,685)		(31,409)
CPRL (Parent Guarantor) | Reportable Legal Entities
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	24		0
Accounts receivable, intercompany	164		125
Short-term advances to affiliates	0		0
Materials and supplies	0		0
Other current assets	0		0
Total current assets	188		125
Long-term advances to affiliates	1,090		1,090
Investments	0		0
Investments in subsidiaries	10,522		11,443
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	4		6
Total assets	11,804		12,664
Current liabilities
Accounts payable and accrued liabilities	146		115
Accounts payable, intercompany	6		4
Short-term advances from affiliates	4,583		5,909
Long-term debt maturing within one year	0		0
Total current liabilities	4,735		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	4,735		6,028
Shareholders’ equity
Share capital	1,993		2,002
Additional paid-in capital	48		42
Accumulated other comprehensive (loss) income	(2,522)		(2,043)
Retained earnings	7,550		6,635
Total shareholders' equity	7,069		6,636
Total liabilities and shareholders’ equity	11,804		12,664
CPRC (Subsidiary Issuer) | Reportable Legal Entities
Current assets
Cash and cash equivalents	37		42
Accounts receivable, net	597		629
Accounts receivable, intercompany	313		167
Short-term advances to affiliates	1,387		1,602
Materials and supplies	144		136
Other current assets	41		39
Total current assets	2,519		2,615
Long-term advances to affiliates	7		5
Investments	32		24
Investments in subsidiaries	11,165		12,003
Properties	10,287		9,579
Goodwill and intangible assets	0		0
Pension asset	1,003		1,243
Other assets	173		57
Deferred income taxes	0		0
Total assets	25,186		25,526
Current liabilities
Accounts payable and accrued liabilities	1,189		1,017
Accounts payable, intercompany	402		344
Short-term advances from affiliates	490		341
Long-term debt maturing within one year	548		506
Total current liabilities	2,629		2,208
Pension and other benefit liabilities	698		639
Long-term advances from affiliates	1,174		1,182
Other long-term liabilities	206		120
Long-term debt	8,145		8,135
Deferred income taxes	1,812		1,799
Total liabilities	14,664		14,083
Shareholders’ equity
Share capital	538		538
Additional paid-in capital	406		1,656
Accumulated other comprehensive (loss) income	(2,522)		(2,043)
Retained earnings	12,100		11,292
Total shareholders' equity	10,522		11,443
Total liabilities and shareholders’ equity	25,186		25,526
Non-Guarantor Subsidiaries | Reportable Legal Entities
Current assets
Cash and cash equivalents	96		19
Accounts receivable, net	184		186
Accounts receivable, intercompany	249		224
Short-term advances to affiliates	3,700		4,651
Materials and supplies	38		37
Other current assets	49		29
Total current assets	4,316		5,146
Long-term advances to affiliates	84		93
Investments	309		179
Investments in subsidiaries	0		0
Properties	8,869		8,839
Goodwill and intangible assets	206		202
Pension asset	0		0
Other assets	278		14
Deferred income taxes	0		0
Total assets	14,062		14,473
Current liabilities
Accounts payable and accrued liabilities	358		317
Accounts payable, intercompany	318		168
Short-term advances from affiliates	14		3
Long-term debt maturing within one year	51		0
Total current liabilities	741		488
Pension and other benefit liabilities	87		79
Long-term advances from affiliates	7		6
Other long-term liabilities	356		117
Long-term debt	13		55
Deferred income taxes	1,693		1,725
Total liabilities	2,897		2,470
Shareholders’ equity
Share capital	4,610		5,946
Additional paid-in capital	265		92
Accumulated other comprehensive (loss) income	581		839
Retained earnings	5,709		5,126
Total shareholders' equity	11,165		12,003
Total liabilities and shareholders’ equity	$ 14,062		$ 14,473