Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	CAD 238	CAD 164
Accounts receivable, net	604	591
Accounts receivable, inter-company	0	0
Short-term advances to affiliates	0	0
Materials and supplies	192	184
Other current assets	85	70
Total current assets	1,119	1,009
Long-term advances to affiliates	0	0
Investments	186	194
Investments in subsidiaries	0	0
Properties	16,703	16,689
Goodwill and intangible assets	195	202
Pension asset	1,261	1,070
Other assets	73	57
Deferred income taxes	0	0
Total assets	19,537	19,221
Current liabilities
Accounts payable and accrued liabilities	1,183	1,322
Accounts payable, inter-company	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	762	25
Total current liabilities	1,945	1,347
Pension and other benefit liabilities	729	734
Long-term advances from affiliates	0	0
Other long-term liabilities	222	284
Long-term debt	7,660	8,659
Deferred income taxes	3,648	3,571
Total liabilities	14,204	14,595
Shareholders’ equity
Share capital	2,038	2,002
Additional paid-in capital	42	52
Accumulated other comprehensive (loss) income	(1,740)	(1,799)
Retained earnings	4,993	4,371
Total Shareholders' equity	5,333	4,626	CAD 4,691	CAD 4,796
Total liabilities and shareholders’ equity	19,537	19,221
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Accounts receivable, inter-company	(431)	(409)
Short-term advances to affiliates	(5,875)	(5,227)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(6,306)	(5,636)
Long-term advances to affiliates	(1,004)	(92)
Investments	0	0
Investments in subsidiaries	(20,548)	(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	(27,869)	(24,501)
Current liabilities
Accounts payable and accrued liabilities	0	0
Accounts payable, inter-company	(431)	(409)
Short-term advances from affiliates	(5,875)	(5,227)
Long-term debt maturing within one year	0	0
Total current liabilities	(6,306)	(5,636)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(1,004)	(92)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(11)	(11)
Total liabilities	(7,321)	(5,739)
Shareholders’ equity
Share capital	(7,873)	(6,860)
Additional paid-in capital	(1,939)	(1,936)
Accumulated other comprehensive (loss) income	1,169	1,087
Retained earnings	(11,905)	(11,053)
Total Shareholders' equity	(20,548)	(18,762)
Total liabilities and shareholders’ equity	(27,869)	(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	95	90
Short-term advances to affiliates	499	500
Materials and supplies	0	0
Other current assets	0	0
Total current assets	594	590
Long-term advances to affiliates	591	1
Investments	0	0
Investments in subsidiaries	9,296	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	10,492	9,116
Current liabilities
Accounts payable and accrued liabilities	84	73
Accounts payable, inter-company	16	14
Short-term advances from affiliates	5,059	4,403
Long-term debt maturing within one year	0	0
Total current liabilities	5,159	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	5,159	4,490
Shareholders’ equity
Share capital	2,038	2,002
Additional paid-in capital	42	52
Accumulated other comprehensive (loss) income	(1,740)	(1,799)
Retained earnings	4,993	4,371
Total Shareholders' equity	5,333	4,626
Total liabilities and shareholders’ equity	10,492	9,116
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	178	100
Accounts receivable, net	440	435
Accounts receivable, inter-company	144	113
Short-term advances to affiliates	559	692
Materials and supplies	158	150
Other current assets	55	38
Total current assets	1,534	1,528
Long-term advances to affiliates	0	0
Investments	43	47
Investments in subsidiaries	11,252	10,249
Properties	8,850	8,756
Goodwill and intangible assets	0	0
Pension asset	1,261	1,070
Other assets	68	48
Deferred income taxes	0	0
Total assets	23,008	21,698
Current liabilities
Accounts payable and accrued liabilities	797	945
Accounts payable, inter-company	283	292
Short-term advances from affiliates	807	816
Long-term debt maturing within one year	762	25
Total current liabilities	2,649	2,078
Pension and other benefit liabilities	657	658
Long-term advances from affiliates	1,004	92
Other long-term liabilities	102	152
Long-term debt	7,606	8,605
Deferred income taxes	1,694	1,600
Total liabilities	13,712	13,185
Shareholders’ equity
Share capital	1,038	1,037
Additional paid-in capital	1,639	1,638
Accumulated other comprehensive (loss) income	(1,740)	(1,799)
Retained earnings	8,359	7,637
Total Shareholders' equity	9,296	8,513
Total liabilities and shareholders’ equity	23,008	21,698
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	60	64
Accounts receivable, net	164	156
Accounts receivable, inter-company	192	206
Short-term advances to affiliates	4,817	4,035
Materials and supplies	34	34
Other current assets	30	32
Total current assets	5,297	4,527
Long-term advances to affiliates	413	91
Investments	143	147
Investments in subsidiaries	0	0
Properties	7,853	7,933
Goodwill and intangible assets	195	202
Pension asset	0	0
Other assets	5	8
Deferred income taxes	0	0
Total assets	13,906	12,908
Current liabilities
Accounts payable and accrued liabilities	302	304
Accounts payable, inter-company	132	103
Short-term advances from affiliates	9	8
Long-term debt maturing within one year	0	0
Total current liabilities	443	415
Pension and other benefit liabilities	72	76
Long-term advances from affiliates	0	0
Other long-term liabilities	120	132
Long-term debt	54	54
Deferred income taxes	1,965	1,982
Total liabilities	2,654	2,659
Shareholders’ equity
Share capital	6,835	5,823
Additional paid-in capital	300	298
Accumulated other comprehensive (loss) income	571	712
Retained earnings	3,546	3,416
Total Shareholders' equity	11,252	10,249
Total liabilities and shareholders’ equity	CAD 13,906	CAD 12,908