Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	CAD 142		CAD 164
Accounts receivable, net	628		591
Accounts receivable, inter-company	0		0
Short-term advances to affiliates	0		0
Materials and supplies	157		184
Other current assets	65		70
Total current assets	992		1,009
Long-term advances to affiliates	0		0
Investments	185		194
Investments in subsidiaries	0		0
Properties	16,700		16,689
Goodwill and intangible assets	187		202
Pension asset	1,356		1,070
Other assets	59		57
Deferred income taxes	0		0
Total assets	19,479		19,221
Current liabilities
Accounts payable and accrued liabilities	1,139		1,322
Due to Related Parties, Current	0		0
Short-term advances from affiliates	0		0
Long-term debt maturing within one year	749		25
Total current liabilities	1,888		1,347
Pension and other benefit liabilities	726		734
Long-term advances from affiliates	0		0
Other long-term liabilities	221		284
Long-term debt	7,384		8,659
Deferred income taxes	3,695		3,571
Total liabilities	13,914		14,595
Shareholders’ equity
Share capital	2,025		2,002
Additional paid-in capital	42		52
Accumulated other comprehensive (loss) income	(1,715)	CAD (1,740)	(1,799)	CAD (1,433)	CAD (1,471)	CAD (1,477)
Retained earnings	5,213		4,371
Total Shareholders' equity	5,565		4,626	CAD 4,669		CAD 4,796
Total liabilities and shareholders’ equity	19,479		19,221
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Accounts receivable, inter-company	(425)		(409)
Short-term advances to affiliates	(5,929)		(5,227)
Materials and supplies	0		0
Other current assets	0		0
Total current assets	(6,354)		(5,636)
Long-term advances to affiliates	(1,001)		(92)
Investments	0		0
Investments in subsidiaries	(20,947)		(18,762)
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	(3)		(11)
Total assets	(28,305)		(24,501)
Current liabilities
Accounts payable and accrued liabilities	0		0
Due to Related Parties, Current	(425)		(409)
Short-term advances from affiliates	(5,929)		(5,227)
Long-term debt maturing within one year	0		0
Total current liabilities	(6,354)		(5,636)
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	(1,001)		(92)
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	(3)		(11)
Total liabilities	(7,358)		(5,739)
Shareholders’ equity
Share capital	(7,898)		(6,860)
Additional paid-in capital	(1,909)		(1,936)
Accumulated other comprehensive (loss) income	1,305		1,087
Retained earnings	(12,445)		(11,053)
Total Shareholders' equity	(20,947)		(18,762)
Total liabilities and shareholders’ equity	(28,305)		(24,501)
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	101		90
Short-term advances to affiliates	500		500
Materials and supplies	0		0
Other current assets	0		0
Total current assets	601		590
Long-term advances to affiliates	591		1
Investments	0		0
Investments in subsidiaries	9,746		8,513
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		1
Deferred income taxes	3		11
Total assets	10,941		9,116
Current liabilities
Accounts payable and accrued liabilities	82		73
Due to Related Parties, Current	15		14
Short-term advances from affiliates	5,279		4,403
Long-term debt maturing within one year	0		0
Total current liabilities	5,376		4,490
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	5,376		4,490
Shareholders’ equity
Share capital	2,025		2,002
Additional paid-in capital	42		52
Accumulated other comprehensive (loss) income	(1,715)		(1,799)
Retained earnings	5,213		4,371
Total Shareholders' equity	5,565		4,626
Total liabilities and shareholders’ equity	10,941		9,116
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	78		100
Accounts receivable, net	464		435
Accounts receivable, inter-company	139		113
Short-term advances to affiliates	560		692
Materials and supplies	124		150
Other current assets	40		38
Total current assets	1,405		1,528
Long-term advances to affiliates	0		0
Investments	43		47
Investments in subsidiaries	11,201		10,249
Properties	8,979		8,756
Goodwill and intangible assets	0		0
Pension asset	1,356		1,070
Other assets	51		48
Deferred income taxes	0		0
Total assets	23,035		21,698
Current liabilities
Accounts payable and accrued liabilities	745		945
Due to Related Parties, Current	282		292
Short-term advances from affiliates	640		816
Long-term debt maturing within one year	749		25
Total current liabilities	2,416		2,078
Pension and other benefit liabilities	657		658
Long-term advances from affiliates	1,001		92
Other long-term liabilities	104		152
Long-term debt	7,334		8,605
Deferred income taxes	1,777		1,600
Total liabilities	13,289		13,185
Shareholders’ equity
Share capital	1,036		1,037
Additional paid-in capital	1,641		1,638
Accumulated other comprehensive (loss) income	(1,716)		(1,799)
Retained earnings	8,785		7,637
Total Shareholders' equity	9,746		8,513
Total liabilities and shareholders’ equity	23,035		21,698
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	64		64
Accounts receivable, net	164		156
Accounts receivable, inter-company	185		206
Short-term advances to affiliates	4,869		4,035
Materials and supplies	33		34
Other current assets	25		32
Total current assets	5,340		4,527
Long-term advances to affiliates	410		91
Investments	142		147
Investments in subsidiaries	0		0
Properties	7,721		7,933
Goodwill and intangible assets	187		202
Pension asset	0		0
Other assets	8		8
Deferred income taxes	0		0
Total assets	13,808		12,908
Current liabilities
Accounts payable and accrued liabilities	312		304
Due to Related Parties, Current	128		103
Short-term advances from affiliates	10		8
Long-term debt maturing within one year	0		0
Total current liabilities	450		415
Pension and other benefit liabilities	69		76
Long-term advances from affiliates	0		0
Other long-term liabilities	117		132
Long-term debt	50		54
Deferred income taxes	1,921		1,982
Total liabilities	2,607		2,659
Shareholders’ equity
Share capital	6,862		5,823
Additional paid-in capital	268		298
Accumulated other comprehensive (loss) income	411		712
Retained earnings	3,660		3,416
Total Shareholders' equity	11,201		10,249
Total liabilities and shareholders’ equity	CAD 13,808		CAD 12,908