Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 145			$ 61
Accounts receivable, net	770			815
Accounts receivable, intercompany	0			0
Short-term advances to affiliates	0			0
Materials and supplies	188			173
Other current assets	83			68
Total current assets	1,186			1,117
Long-term advances to affiliates	0			0
Investments	215			203
Investments in subsidiaries	0			0
Properties	18,909		$ 18,406	18,418
Goodwill and intangible assets	195			202
Pension asset	1,572			1,243
Other assets	462		470	71
Deferred income taxes	0			0
Total assets	22,539			21,254
Current liabilities
Accounts payable and accrued liabilities	1,415		1,507	1,449
Accounts payable, intercompany	0			0
Short-term advances from affiliates	0			0
Long-term debt maturing within one year	675			506
Total current liabilities	2,090			1,955
Pension and other benefit liabilities	712			718
Long-term advances from affiliates	0			0
Other long-term liabilities	579		574	237
Long-term debt	8,308			8,190
Deferred income taxes	3,635		3,515	3,518
Total liabilities	15,324			14,618
Shareholders’ equity
Share capital	1,982			2,002
Additional paid-in capital	45			42
Accumulated other comprehensive (loss) income	(1,992)	$ (2,009)		(2,043)	$ (1,654)	$ (1,673)	$ (1,741)
Retained earnings	7,180		6,630	6,635
Total shareholders' equity	7,215	$ 7,157	$ 6,631	6,636	$ 7,128	$ 6,574	$ 6,437
Total liabilities and shareholders’ equity	22,539			21,254
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0			0
Accounts receivable, net	0			0
Accounts receivable, intercompany	(526)			(516)
Short-term advances to affiliates	(6,017)			(6,253)
Materials and supplies	0			0
Other current assets	0			0
Total current assets	(6,543)			(6,769)
Long-term advances to affiliates	(1,182)			(1,188)
Investments	0			0
Investments in subsidiaries	(24,175)			(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	(31,905)			(31,409)
Current liabilities
Accounts payable and accrued liabilities	0			0
Accounts payable, intercompany	(526)			(516)
Short-term advances from affiliates	(6,017)			(6,253)
Long-term debt maturing within one year	0			0
Total current liabilities	(6,543)			(6,769)
Pension and other benefit liabilities	0			0
Long-term advances from affiliates	(1,182)			(1,188)
Other long-term liabilities	0			0
Long-term debt	0			0
Deferred income taxes	(5)			(6)
Total liabilities	(7,730)			(7,963)
Shareholders’ equity
Share capital	(6,608)			(6,484)
Additional paid-in capital	(1,744)			(1,748)
Accumulated other comprehensive (loss) income	1,300			1,204
Retained earnings	(17,123)			(16,418)
Total shareholders' equity	(24,175)			(23,446)
Total liabilities and shareholders’ equity	(31,905)			(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	158			125
Short-term advances to affiliates	0			0
Materials and supplies	0			0
Other current assets	0			0
Total current assets	158			125
Long-term advances to affiliates	1,090			1,090
Investments	0			0
Investments in subsidiaries	11,748			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	13,001			12,664
Current liabilities
Accounts payable and accrued liabilities	128			115
Accounts payable, intercompany	7			4
Short-term advances from affiliates	5,651			5,909
Long-term debt maturing within one year	0			0
Total current liabilities	5,786			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	5,786			6,028
Shareholders’ equity
Share capital	1,982			2,002
Additional paid-in capital	45			42
Accumulated other comprehensive (loss) income	(1,992)			(2,043)
Retained earnings	7,180			6,635
Total shareholders' equity	7,215			6,636
Total liabilities and shareholders’ equity	13,001			12,664
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	45			42
Accounts receivable, net	581			629
Accounts receivable, intercompany	136			167
Short-term advances to affiliates	1,099			1,602
Materials and supplies	150			136
Other current assets	51			39
Total current assets	2,062			2,615
Long-term advances to affiliates	6			5
Investments	31			24
Investments in subsidiaries	12,427			12,003
Properties	10,080			9,579
Goodwill and intangible assets	0			0
Pension asset	1,572			1,243
Other assets	167			57
Deferred income taxes	0			0
Total assets	26,345			25,526
Current liabilities
Accounts payable and accrued liabilities	926			1,017
Accounts payable, intercompany	383			344
Short-term advances from affiliates	363			341
Long-term debt maturing within one year	634			506
Total current liabilities	2,306			2,208
Pension and other benefit liabilities	640			639
Long-term advances from affiliates	1,176			1,182
Other long-term liabilities	224			120
Long-term debt	8,295			8,135
Deferred income taxes	1,956			1,799
Total liabilities	14,597			14,083
Shareholders’ equity
Share capital	537			538
Additional paid-in capital	1,648			1,656
Accumulated other comprehensive (loss) income	(1,992)			(2,043)
Retained earnings	11,555			11,292
Total shareholders' equity	11,748			11,443
Total liabilities and shareholders’ equity	26,345			25,526
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	100			19
Accounts receivable, net	189			186
Accounts receivable, intercompany	232			224
Short-term advances to affiliates	4,918			4,651
Materials and supplies	38			37
Other current assets	32			29
Total current assets	5,509			5,146
Long-term advances to affiliates	86			93
Investments	184			179
Investments in subsidiaries	0			0
Properties	8,829			8,839
Goodwill and intangible assets	195			202
Pension asset	0			0
Other assets	295			14
Deferred income taxes	0			0
Total assets	15,098			14,473
Current liabilities
Accounts payable and accrued liabilities	361			317
Accounts payable, intercompany	136			168
Short-term advances from affiliates	3			3
Long-term debt maturing within one year	41			0
Total current liabilities	541			488
Pension and other benefit liabilities	72			79
Long-term advances from affiliates	6			6
Other long-term liabilities	355			117
Long-term debt	13			55
Deferred income taxes	1,684			1,725
Total liabilities	2,671			2,470
Shareholders’ equity
Share capital	6,071			5,946
Additional paid-in capital	96			92
Accumulated other comprehensive (loss) income	692			839
Retained earnings	5,568			5,126
Total shareholders' equity	12,427			12,003
Total liabilities and shareholders’ equity	$ 15,098			$ 14,473