Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 45			$ 61
Accounts receivable, net	795			815
Accounts receivable, intercompany	0			0
Short-term advances to affiliates	0			0
Materials and supplies	195			173
Other current assets	80			68
Total current assets	1,115			1,117
Long-term advances to affiliates	0			0
Investments	210			203
Investments in subsidiaries	0			0
Properties	18,489		$ 18,406	18,418
Goodwill and intangible assets	193			202
Pension asset	1,460			1,243
Other assets	466		470	71
Deferred income taxes	0			0
Total assets	21,933			21,254
Current liabilities
Accounts payable and accrued liabilities	1,401		1,507	1,449
Accounts payable, intercompany	0			0
Short-term advances from affiliates	0			0
Long-term debt maturing within one year	273			506
Total current liabilities	1,674			1,955
Pension and other benefit liabilities	713			718
Long-term advances from affiliates	0			0
Other long-term liabilities	598		574	237
Long-term debt	8,266			8,190
Deferred income taxes	3,525		3,515	3,518
Total liabilities	14,776			14,618
Shareholders’ equity
Share capital	1,996			2,002
Additional paid-in capital	45			42
Accumulated other comprehensive (loss) income	(2,009)	$ (2,027)		(2,043)	$ (1,673)	$ (1,705)	$ (1,741)
Retained earnings	7,125		6,630	6,635
Total shareholders' equity	7,157	$ 6,814	$ 6,631	6,636	$ 6,574	$ 6,434	$ 6,437
Total liabilities and shareholders’ equity	21,933			21,254
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0			0
Accounts receivable, net	0			0
Accounts receivable, intercompany	(504)			(516)
Short-term advances to affiliates	(6,107)			(6,253)
Materials and supplies	0			0
Other current assets	0			0
Total current assets	(6,611)			(6,769)
Long-term advances to affiliates	(1,181)			(1,188)
Investments	0			0
Investments in subsidiaries	(24,044)			(23,446)
Properties	0			0
Goodwill and intangible assets	0			0
Pension asset	0			0
Other assets	0			0
Deferred income taxes	(5)			(6)
Total assets	(31,841)			(31,409)
Current liabilities
Accounts payable and accrued liabilities	0			0
Accounts payable, intercompany	(504)			(516)
Short-term advances from affiliates	(6,107)			(6,253)
Long-term debt maturing within one year	0			0
Total current liabilities	(6,611)			(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	(5)			(6)
Total liabilities	(7,797)			(7,963)
Shareholders’ equity
Share capital	(6,608)			(6,484)
Additional paid-in capital	(1,740)			(1,748)
Accumulated other comprehensive (loss) income	1,378			1,204
Retained earnings	(17,074)			(16,418)
Total shareholders' equity	(24,044)			(23,446)
Total liabilities and shareholders’ equity	(31,841)			(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, intercompany	153			125
Short-term advances to affiliates	0			0
Materials and supplies	0			0
Other current assets	0			0
Total current assets	153			125
Long-term advances to affiliates	1,090			1,090
Investments	0			0
Investments in subsidiaries	11,819			11,443
Properties	0			0
Goodwill and intangible assets	0			0
Pension asset	0			0
Other assets	0			0
Deferred income taxes	5			6
Total assets	13,067			12,664
Current liabilities
Accounts payable and accrued liabilities	156			115
Accounts payable, intercompany	5			4
Short-term advances from affiliates	5,749			5,909
Long-term debt maturing within one year	0			0
Total current liabilities	5,910			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	5,910			6,028
Shareholders’ equity
Share capital	1,996			2,002
Additional paid-in capital	45			42
Accumulated other comprehensive (loss) income	(2,009)			(2,043)
Retained earnings	7,125			6,635
Total shareholders' equity	7,157			6,636
Total liabilities and shareholders’ equity	13,067			12,664
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	20			42
Accounts receivable, net	593			629
Accounts receivable, intercompany	146			167
Short-term advances to affiliates	1,197			1,602
Materials and supplies	158			136
Other current assets	61			39
Total current assets	2,175			2,615
Long-term advances to affiliates	6			5
Investments	31			24
Investments in subsidiaries	12,225			12,003
Properties	9,761			9,579
Goodwill and intangible assets	0			0
Pension asset	1,460			1,243
Other assets	161			57
Deferred income taxes	0			0
Total assets	25,819			25,526
Current liabilities
Accounts payable and accrued liabilities	872			1,017
Accounts payable, intercompany	354			344
Short-term advances from affiliates	356			341
Long-term debt maturing within one year	273			506
Total current liabilities	1,855			2,208
Pension and other benefit liabilities	638			639
Long-term advances from affiliates	1,175			1,182
Other long-term liabilities	234			120
Long-term debt	8,213			8,135
Deferred income taxes	1,885			1,799
Total liabilities	14,000			14,083
Shareholders’ equity
Share capital	537			538
Additional paid-in capital	1,645			1,656
Accumulated other comprehensive (loss) income	(2,009)			(2,043)
Retained earnings	11,646			11,292
Total shareholders' equity	11,819			11,443
Total liabilities and shareholders’ equity	25,819			25,526
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	25			19
Accounts receivable, net	202			186
Accounts receivable, intercompany	205			224
Short-term advances to affiliates	4,910			4,651
Materials and supplies	37			37
Other current assets	19			29
Total current assets	5,398			5,146
Long-term advances to affiliates	85			93
Investments	179			179
Investments in subsidiaries	0			0
Properties	8,728			8,839
Goodwill and intangible assets	193			202
Pension asset	0			0
Other assets	305			14
Deferred income taxes	0			0
Total assets	14,888			14,473
Current liabilities
Accounts payable and accrued liabilities	373			317
Accounts payable, intercompany	145			168
Short-term advances from affiliates	2			3
Long-term debt maturing within one year	0			0
Total current liabilities	520			488
Pension and other benefit liabilities	75			79
Long-term advances from affiliates	6			6
Other long-term liabilities	364			117
Long-term debt	53			55
Deferred income taxes	1,645			1,725
Total liabilities	2,663			2,470
Shareholders’ equity
Share capital	6,071			5,946
Additional paid-in capital	95			92
Accumulated other comprehensive (loss) income	631			839
Retained earnings	5,428			5,126
Total shareholders' equity	12,225			12,003
Total liabilities and shareholders’ equity	$ 14,888			$ 14,473