Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Detail) - CAD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 61	$ 338
Accounts receivable, net	815	687
Accounts receivable, intercompany	0	0
Short-term advances to affiliates	0	0
Materials and supplies	173	152
Other current assets	68	97
Total current assets	1,117	1,274
Long-term advances to affiliates	0	0
Investments	203	182
Investments in subsidiaries	0	0
Properties	18,418	17,016
Goodwill and intangible assets	202	187	$ 202
Pension asset	1,243	1,407
Other assets	71	69
Deferred income taxes	0	0
Total assets	21,254	20,135
Current liabilities
Accounts payable and accrued liabilities	1,449	1,238
Accounts payable, intercompany	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	506	746
Total current liabilities	1,955	1,984
Pension and other benefit liabilities	718	749
Long-term advances from affiliates	0	0
Other long-term liabilities	237	231
Long-term debt	8,190	7,413
Deferred income taxes	3,518	3,321
Total liabilities	14,618	13,698
Shareholders’ equity
Share capital	2,002	2,032
Additional paid-in capital	42	43
Accumulated other comprehensive (loss) income	(2,043)	(1,741)	(1,799)
Retained earnings	6,635	6,103
Total shareholders' equity	6,636	6,437	$ 4,626	$ 4,796
Total liabilities and shareholders’ equity	21,254	20,135
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, intercompany	(516)	(465)
Short-term advances to affiliates	(6,253)	(6,500)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(6,769)	(6,965)
Long-term advances to affiliates	(1,188)	(1,000)
Investments	0	0
Investments in subsidiaries	(23,446)	(22,745)
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	(6)	(3)
Total assets	(31,409)	(30,713)
Current liabilities
Accounts payable and accrued liabilities	0	0
Accounts payable, intercompany	(516)	(465)
Short-term advances from affiliates	(6,253)	(6,500)
Long-term debt maturing within one year	0	0
Total current liabilities	(6,769)	(6,965)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(1,188)	(1,000)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(6)	(3)
Total liabilities	(7,963)	(7,968)
Shareholders’ equity
Share capital	(6,484)	(7,767)
Additional paid-in capital	(1,748)	(1,902)
Accumulated other comprehensive (loss) income	1,204	1,325
Retained earnings	(16,418)	(14,401)
Total shareholders' equity	(23,446)	(22,745)
Total liabilities and shareholders’ equity	(31,409)	(30,713)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, intercompany	125	97
Short-term advances to affiliates	0	500
Materials and supplies	0	0
Other current assets	0	0
Total current assets	125	597
Long-term advances to affiliates	1,090	590
Investments	0	0
Investments in subsidiaries	11,443	10,623
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	6	3
Total assets	12,664	11,813
Current liabilities
Accounts payable and accrued liabilities	115	82
Accounts payable, intercompany	4	3
Short-term advances from affiliates	5,909	5,291
Long-term debt maturing within one year	0	0
Total current liabilities	6,028	5,376
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	6,028	5,376
Shareholders’ equity
Share capital	2,002	2,032
Additional paid-in capital	42	43
Accumulated other comprehensive (loss) income	(2,043)	(1,741)
Retained earnings	6,635	6,103
Total shareholders' equity	6,636	6,437
Total liabilities and shareholders’ equity	12,664	11,813
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	42	241
Accounts receivable, net	629	508
Accounts receivable, intercompany	167	153
Short-term advances to affiliates	1,602	1,004
Materials and supplies	136	120
Other current assets	39	31
Total current assets	2,615	2,057
Long-term advances to affiliates	5	0
Investments	24	27
Investments in subsidiaries	12,003	12,122
Properties	9,579	8,982
Goodwill and intangible assets	0	0
Pension asset	1,243	1,407
Other assets	57	56
Deferred income taxes	0	0
Total assets	25,526	24,651
Current liabilities
Accounts payable and accrued liabilities	1,017	844
Accounts payable, intercompany	344	309
Short-term advances from affiliates	341	1,185
Long-term debt maturing within one year	506	746
Total current liabilities	2,208	3,084
Pension and other benefit liabilities	639	672
Long-term advances from affiliates	1,182	1,000
Other long-term liabilities	120	108
Long-term debt	8,135	7,362
Deferred income taxes	1,799	1,802
Total liabilities	14,083	14,028
Shareholders’ equity
Share capital	538	1,037
Additional paid-in capital	1,656	1,643
Accumulated other comprehensive (loss) income	(2,043)	(1,742)
Retained earnings	11,292	9,685
Total shareholders' equity	11,443	10,623
Total liabilities and shareholders’ equity	25,526	24,651
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	19	97
Accounts receivable, net	186	179
Accounts receivable, intercompany	224	215
Short-term advances to affiliates	4,651	4,996
Materials and supplies	37	32
Other current assets	29	66
Total current assets	5,146	5,585
Long-term advances to affiliates	93	410
Investments	179	155
Investments in subsidiaries	0	0
Properties	8,839	8,034
Goodwill and intangible assets	202	187
Pension asset	0	0
Other assets	14	13
Deferred income taxes	0	0
Total assets	14,473	14,384
Current liabilities
Accounts payable and accrued liabilities	317	312
Accounts payable, intercompany	168	153
Short-term advances from affiliates	3	24
Long-term debt maturing within one year	0	0
Total current liabilities	488	489
Pension and other benefit liabilities	79	77
Long-term advances from affiliates	6	0
Other long-term liabilities	117	123
Long-term debt	55	51
Deferred income taxes	1,725	1,522
Total liabilities	2,470	2,262
Shareholders’ equity
Share capital	5,946	6,730
Additional paid-in capital	92	259
Accumulated other comprehensive (loss) income	839	417
Retained earnings	5,126	4,716
Total shareholders' equity	12,003	12,122
Total liabilities and shareholders’ equity	$ 14,473	$ 14,384