Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Detail) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	CAD 338	CAD 164
Accounts receivable, net	687	591
Accounts receivable, intercompany	0	0
Short-term advances to affiliates	0	0
Materials and supplies	152	184
Other current assets	97	70
Total current assets	1,274	1,009
Long-term advances to affiliates	0	0
Investments	182	194
Investments in subsidiaries	0	0
Properties	17,016	16,689
Goodwill and intangible assets	187	202	CAD 211
Pension asset	1,407	1,070
Other assets	69	57
Deferred income taxes	0	0
Total assets	20,135	19,221
Current liabilities
Accounts payable and accrued liabilities	1,238	1,322
Due to Related Parties, Current	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	746	25
Total current liabilities	1,984	1,347
Pension and other benefit liabilities	749	734
Long-term advances from affiliates	0	0
Other long-term liabilities	231	284
Long-term debt	7,413	8,659
Deferred income taxes	3,321	3,571
Total liabilities	13,698	14,595
Shareholders’ equity
Share capital	2,032	2,002
Additional paid-in capital	43	52
Accumulated other comprehensive (loss) income	(1,741)	(1,799)	(1,477)
Retained earnings	6,103	4,371
Total Shareholders' equity	6,437	4,626	CAD 4,796	CAD 5,610
Total liabilities and shareholders’ equity	20,135	19,221
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, intercompany	(465)	(409)
Short-term advances to affiliates	(6,500)	(5,227)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(6,965)	(5,636)
Long-term advances to affiliates	(1,000)	(92)
Investments	0	0
Investments in subsidiaries	(22,745)	(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	(30,713)	(24,501)
Current liabilities
Accounts payable and accrued liabilities	0	0
Due to Related Parties, Current	(465)	(409)
Short-term advances from affiliates	(6,500)	(5,227)
Long-term debt maturing within one year	0	0
Total current liabilities	(6,965)	(5,636)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(1,000)	(92)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(3)	(11)
Total liabilities	(7,968)	(5,739)
Shareholders’ equity
Share capital	(7,767)	(6,860)
Additional paid-in capital	(1,902)	(1,936)
Accumulated other comprehensive (loss) income	1,325	1,087
Retained earnings	(14,401)	(11,053)
Total Shareholders' equity	(22,745)	(18,762)
Total liabilities and shareholders’ equity	(30,713)	(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, intercompany	97	90
Short-term advances to affiliates	500	500
Materials and supplies	0	0
Other current assets	0	0
Total current assets	597	590
Long-term advances to affiliates	590	1
Investments	0	0
Investments in subsidiaries	10,623	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	11,813	9,116
Current liabilities
Accounts payable and accrued liabilities	82	73
Due to Related Parties, Current	3	14
Short-term advances from affiliates	5,291	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	2,032	2,002
Additional paid-in capital	43	52
Accumulated other comprehensive (loss) income	(1,741)	(1,799)
Retained earnings	6,103	4,371
Total Shareholders' equity	6,437	4,626
Total liabilities and shareholders’ equity	11,813	9,116
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	241	100
Accounts receivable, net	508	435
Accounts receivable, intercompany	153	113
Short-term advances to affiliates	1,004	692
Materials and supplies	120	150
Other current assets	31	38
Total current assets	2,057	1,528
Long-term advances to affiliates	0	0
Investments	27	47
Investments in subsidiaries	12,122	10,249
Properties	8,982	8,756
Goodwill and intangible assets	0	0
Pension asset	1,407	1,070
Other assets	56	48
Deferred income taxes	0	0
Total assets	24,651	21,698
Current liabilities
Accounts payable and accrued liabilities	844	945
Due to Related Parties, Current	309	292
Short-term advances from affiliates	1,185	816
Long-term debt maturing within one year	746	25
Total current liabilities	3,084	2,078
Pension and other benefit liabilities	672	658
Long-term advances from affiliates	1,000	92
Other long-term liabilities	108	152
Long-term debt	7,362	8,605
Deferred income taxes	1,802	1,600
Total liabilities	14,028	13,185
Shareholders’ equity
Share capital	1,037	1,037
Additional paid-in capital	1,643	1,638
Accumulated other comprehensive (loss) income	(1,742)	(1,799)
Retained earnings	9,685	7,637
Total Shareholders' equity	10,623	8,513
Total liabilities and shareholders’ equity	24,651	21,698
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	97	64
Accounts receivable, net	179	156
Accounts receivable, intercompany	215	206
Short-term advances to affiliates	4,996	4,035
Materials and supplies	32	34
Other current assets	66	32
Total current assets	5,585	4,527
Long-term advances to affiliates	410	91
Investments	155	147
Investments in subsidiaries	0	0
Properties	8,034	7,933
Goodwill and intangible assets	187	202
Pension asset	0	0
Other assets	13	8
Deferred income taxes	0	0
Total assets	14,384	12,908
Current liabilities
Accounts payable and accrued liabilities	312	304
Due to Related Parties, Current	153	103
Short-term advances from affiliates	24	8
Long-term debt maturing within one year	0	0
Total current liabilities	489	415
Pension and other benefit liabilities	77	76
Long-term advances from affiliates	0	0
Other long-term liabilities	123	132
Long-term debt	51	54
Deferred income taxes	1,522	1,982
Total liabilities	2,262	2,659
Shareholders’ equity
Share capital	6,730	5,823
Additional paid-in capital	259	298
Accumulated other comprehensive (loss) income	417	712
Retained earnings	4,716	3,416
Total Shareholders' equity	12,122	10,249
Total liabilities and shareholders’ equity	CAD 14,384	CAD 12,908