Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 247	$ 133
Accounts receivable, net	885	805
Accounts receivable, intercompany	0	0
Short-term advances to affiliates	0	0
Materials and supplies	177	182
Other current assets	98	90
Total current assets	1,407	1,210
Long-term advances to affiliates	0	0
Investments	369	341
Investments in subsidiaries	0	0
Properties	19,900	19,156
Goodwill and intangible assets	223	206
Pension asset	1,111	1,003
Other assets	478	451
Deferred income taxes	0	0
Total assets	23,488	22,367
Current liabilities
Accounts payable and accrued liabilities	1,528	1,693
Accounts payable, intercompany	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	266	599
Total current liabilities	1,794	2,292
Pension and other benefit liabilities	790	785
Long-term advances from affiliates	0	0
Other long-term liabilities	541	562
Long-term debt	9,804	8,158
Deferred income taxes	3,604	3,501
Total liabilities	16,533	15,298
Shareholders’ equity
Share capital	1,985	1,993
Additional paid-in capital	51	48
Accumulated other comprehensive (loss) income	(2,480)	(2,522)	$ (2,027)	$ (2,043)
Retained earnings	7,399	7,550
Total shareholders' equity	6,955	7,069	$ 6,814
Total liabilities and shareholders’ equity	23,488	22,367
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, intercompany	(589)	(726)
Short-term advances to affiliates	(5,765)	(5,087)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(6,354)	(5,813)
Long-term advances to affiliates	(1,190)	(1,181)
Investments	0	0
Investments in subsidiaries	(22,747)	(21,687)
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	(5)	(4)
Total assets	(30,296)	(28,685)
Current liabilities
Accounts payable and accrued liabilities	0	0
Accounts payable, intercompany	(589)	(726)
Short-term advances from affiliates	(5,765)	(5,087)
Long-term debt maturing within one year	0	0
Total current liabilities	(6,354)	(5,813)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(1,190)	(1,181)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(5)	(4)
Total liabilities	(7,549)	(6,998)
Shareholders’ equity
Share capital	(5,148)	(5,148)
Additional paid-in capital	(678)	(671)
Accumulated other comprehensive (loss) income	1,408	1,941
Retained earnings	(18,329)	(17,809)
Total shareholders' equity	(22,747)	(21,687)
Total liabilities and shareholders’ equity	(30,296)	(28,685)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	24
Accounts receivable, intercompany	172	164
Short-term advances to affiliates	0	0
Materials and supplies	0	0
Other current assets	0	0
Total current assets	172	188
Long-term advances to affiliates	1,090	1,090
Investments	0	0
Investments in subsidiaries	10,886	10,522
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	5	4
Total assets	12,153	11,804
Current liabilities
Accounts payable and accrued liabilities	113	146
Accounts payable, intercompany	7	6
Short-term advances from affiliates	5,078	4,583
Long-term debt maturing within one year	0	0
Total current liabilities	5,198	4,735
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	5,198	4,735
Shareholders’ equity
Share capital	1,985	1,993
Additional paid-in capital	51	48
Accumulated other comprehensive (loss) income	(2,480)	(2,522)
Retained earnings	7,399	7,550
Total shareholders' equity	6,955	7,069
Total liabilities and shareholders’ equity	12,153	11,804
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	119	37
Accounts receivable, net	670	597
Accounts receivable, intercompany	249	313
Short-term advances to affiliates	1,891	1,387
Materials and supplies	134	144
Other current assets	54	41
Total current assets	3,117	2,519
Long-term advances to affiliates	8	7
Investments	29	32
Investments in subsidiaries	11,861	11,165
Properties	10,446	10,287
Goodwill and intangible assets	0	0
Pension asset	1,111	1,003
Other assets	179	173
Deferred income taxes	0	0
Total assets	26,751	25,186
Current liabilities
Accounts payable and accrued liabilities	1,025	1,189
Accounts payable, intercompany	333	402
Short-term advances from affiliates	664	490
Long-term debt maturing within one year	203	548
Total current liabilities	2,225	2,629
Pension and other benefit liabilities	695	698
Long-term advances from affiliates	1,181	1,174
Other long-term liabilities	180	206
Long-term debt	9,804	8,145
Deferred income taxes	1,780	1,812
Total liabilities	15,865	14,664
Shareholders’ equity
Share capital	538	538
Additional paid-in capital	411	406
Accumulated other comprehensive (loss) income	(2,480)	(2,522)
Retained earnings	12,417	12,100
Total shareholders' equity	10,886	10,522
Total liabilities and shareholders’ equity	26,751	25,186
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	128	96
Accounts receivable, net	215	184
Accounts receivable, intercompany	168	249
Short-term advances to affiliates	3,874	3,700
Materials and supplies	43	38
Other current assets	44	49
Total current assets	4,472	4,316
Long-term advances to affiliates	92	84
Investments	340	309
Investments in subsidiaries	0	0
Properties	9,454	8,869
Goodwill and intangible assets	223	206
Pension asset	0	0
Other assets	299	278
Deferred income taxes	0	0
Total assets	14,880	14,062
Current liabilities
Accounts payable and accrued liabilities	390	358
Accounts payable, intercompany	249	318
Short-term advances from affiliates	23	14
Long-term debt maturing within one year	63	51
Total current liabilities	725	741
Pension and other benefit liabilities	95	87
Long-term advances from affiliates	9	7
Other long-term liabilities	361	356
Long-term debt	0	13
Deferred income taxes	1,829	1,693
Total liabilities	3,019	2,897
Shareholders’ equity
Share capital	4,610	4,610
Additional paid-in capital	267	265
Accumulated other comprehensive (loss) income	1,072	581
Retained earnings	5,912	5,709
Total shareholders' equity	11,861	11,165
Total liabilities and shareholders’ equity	$ 14,880	$ 14,062