Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	CAD 201	CAD 164
Accounts receivable, net	631	591
Accounts receivable, inter-company	0	0
Short-term advances to affiliates	0	0
Materials and supplies	201	184
Other current assets	77	70
Total current assets	1,110	1,009
Long-term advances to affiliates	0	0
Investments	183	194
Investments in subsidiaries	0	0
Properties	16,661	16,689
Goodwill and intangible assets	200	202
Pension asset	1,165	1,070
Other assets	78	57
Deferred income taxes	0	0
Total assets	19,397	19,221
Current liabilities
Accounts payable and accrued liabilities	1,148	1,322
Accounts payable, inter-company	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	31	25
Total current liabilities	1,179	1,347
Pension and other benefit liabilities	730	734
Long-term advances from affiliates	0	0
Other long-term liabilities	227	284
Long-term debt	8,583	8,659
Deferred income taxes	3,640	3,571
Total liabilities	14,359	14,595
Shareholders’ equity
Share capital	2,036	2,002
Additional paid-in capital	42	52
Accumulated other comprehensive (loss) income	(1,769)	(1,799)
Retained earnings	4,729	4,371
Total Shareholders' equity	5,038	4,626	CAD 5,290	CAD 4,796
Total liabilities and shareholders’ equity	19,397	19,221
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, inter-company	(438)	(409)
Short-term advances to affiliates	(5,180)	(5,227)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(5,618)	(5,636)
Long-term advances to affiliates	(91)	(92)
Investments	0	0
Investments in subsidiaries	(19,286)	(18,762)
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	(11)	(11)
Total assets	(25,006)	(24,501)
Current liabilities
Accounts payable and accrued liabilities	0	0
Accounts payable, inter-company	(438)	(409)
Short-term advances from affiliates	(5,180)	(5,227)
Long-term debt maturing within one year	0	0
Total current liabilities	(5,618)	(5,636)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(91)	(92)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(11)	(11)
Total liabilities	(5,720)	(5,739)
Shareholders’ equity
Share capital	(6,928)	(6,860)
Additional paid-in capital	(1,937)	(1,936)
Accumulated other comprehensive (loss) income	1,098	1,087
Retained earnings	(11,519)	(11,053)
Total Shareholders' equity	(19,286)	(18,762)
Total liabilities and shareholders’ equity	(25,006)	(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	92	90
Short-term advances to affiliates	500	500
Materials and supplies	0	0
Other current assets	0	0
Total current assets	592	590
Long-term advances to affiliates	1	1
Investments	0	0
Investments in subsidiaries	8,882	8,513
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	1
Deferred income taxes	11	11
Total assets	9,486	9,116
Current liabilities
Accounts payable and accrued liabilities	73	73
Accounts payable, inter-company	17	14
Short-term advances from affiliates	4,358	4,403
Long-term debt maturing within one year	0	0
Total current liabilities	4,448	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	4,448	4,490
Shareholders’ equity
Share capital	2,036	2,002
Additional paid-in capital	42	52
Accumulated other comprehensive (loss) income	(1,769)	(1,799)
Retained earnings	4,729	4,371
Total Shareholders' equity	5,038	4,626
Total liabilities and shareholders’ equity	9,486	9,116
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	83	100
Accounts receivable, net	447	435
Accounts receivable, inter-company	152	113
Short-term advances to affiliates	513	692
Materials and supplies	167	150
Other current assets	52	38
Total current assets	1,414	1,528
Long-term advances to affiliates	0	0
Investments	40	47
Investments in subsidiaries	10,404	10,249
Properties	8,763	8,756
Goodwill and intangible assets	0	0
Pension asset	1,165	1,070
Other assets	69	48
Deferred income taxes	0	0
Total assets	21,855	21,698
Current liabilities
Accounts payable and accrued liabilities	804	945
Accounts payable, inter-company	281	292
Short-term advances from affiliates	813	816
Long-term debt maturing within one year	31	25
Total current liabilities	1,929	2,078
Pension and other benefit liabilities	656	658
Long-term advances from affiliates	91	92
Other long-term liabilities	96	152
Long-term debt	8,529	8,605
Deferred income taxes	1,672	1,600
Total liabilities	12,973	13,185
Shareholders’ equity
Share capital	1,037	1,037
Additional paid-in capital	1,637	1,638
Accumulated other comprehensive (loss) income	(1,770)	(1,799)
Retained earnings	7,978	7,637
Total Shareholders' equity	8,882	8,513
Total liabilities and shareholders’ equity	21,855	21,698
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	118	64
Accounts receivable, net	184	156
Accounts receivable, inter-company	194	206
Short-term advances to affiliates	4,167	4,035
Materials and supplies	34	34
Other current assets	25	32
Total current assets	4,722	4,527
Long-term advances to affiliates	90	91
Investments	143	147
Investments in subsidiaries	0	0
Properties	7,898	7,933
Goodwill and intangible assets	200	202
Pension asset	0	0
Other assets	9	8
Deferred income taxes	0	0
Total assets	13,062	12,908
Current liabilities
Accounts payable and accrued liabilities	271	304
Accounts payable, inter-company	140	103
Short-term advances from affiliates	9	8
Long-term debt maturing within one year	0	0
Total current liabilities	420	415
Pension and other benefit liabilities	74	76
Long-term advances from affiliates	0	0
Other long-term liabilities	131	132
Long-term debt	54	54
Deferred income taxes	1,979	1,982
Total liabilities	2,658	2,659
Shareholders’ equity
Share capital	5,891	5,823
Additional paid-in capital	300	298
Accumulated other comprehensive (loss) income	672	712
Retained earnings	3,541	3,416
Total Shareholders' equity	10,404	10,249
Total liabilities and shareholders’ equity	CAD 13,062	CAD 12,908