Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	CAD 571	CAD 650	CAD 184	CAD 226
Accounts receivable, net	629	645
Accounts receivable, inter-company	0	0
Short-term advances to affiliates	0	0
Materials and supplies	181	188
Other current assets	69	54
Total current assets	1,450	1,537
Long-term advances to affiliates	0	0
Investments	148	152
Investments in subsidiaries	0	0
Properties	16,013	16,273
Goodwill and intangible assets	196	211
Pension asset	1,489	1,401
Other assets	53	63
Deferred income taxes	0	0
Total assets	19,349	19,637
Current liabilities
Accounts payable and accrued liabilities	1,143	1,417
Accounts payable, inter-company	0	0
Short-term advances from affiliates	0	0
Long-term debt maturing within one year	23	30
Total current liabilities	1,166	1,447
Pension and other benefit liabilities	750	758
Long-term advances from affiliates	0	0
Other long-term liabilities	291	318
Long-term debt	8,430	8,927
Deferred income taxes	3,422	3,391
Total liabilities	14,059	14,841
Shareholders’ equity
Share capital	2,065	2,058
Additional paid-in capital	48	43
Accumulated other comprehensive (loss) income	(1,481)	(1,477)
Retained earnings	4,658	4,172
Total Shareholders' equity	5,290	4,796	5,418	5,610
Total liabilities and shareholders’ equity	19,349	19,637
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Accounts receivable, inter-company	(341)	(429)
Short-term advances to affiliates	(3,539)	(3,558)
Materials and supplies	0	0
Other current assets	0	0
Total current assets	(3,880)	(3,987)
Long-term advances to affiliates	(1,061)	(1,084)
Investments	0	0
Investments in subsidiaries	(17,605)	(17,350)
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	(16)	(25)
Total assets	(22,562)	(22,446)
Current liabilities
Accounts payable and accrued liabilities	0	0
Accounts payable, inter-company	(341)	(429)
Short-term advances from affiliates	(3,539)	(3,558)
Long-term debt maturing within one year	0	0
Total current liabilities	(3,880)	(3,987)
Pension and other benefit liabilities	0	0
Long-term advances from affiliates	(1,061)	(1,084)
Other long-term liabilities	0	0
Long-term debt	0	0
Deferred income taxes	(16)	(25)
Total liabilities	(4,957)	(5,096)
Shareholders’ equity
Share capital	(6,496)	(6,502)
Additional paid-in capital	(2,196)	(2,181)
Accumulated other comprehensive (loss) income	912	637
Retained earnings	(9,825)	(9,304)
Total Shareholders' equity	(17,605)	(17,350)
Total liabilities and shareholders’ equity	(22,562)	(22,446)
CPRL (Parent Guarantor) [Member]
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Accounts receivable, inter-company	61	59
Short-term advances to affiliates	45	0
Materials and supplies	0	0
Other current assets	0	0
Total current assets	106	59
Long-term advances to affiliates	501	501
Investments	0	0
Investments in subsidiaries	7,948	7,518
Properties	0	0
Goodwill and intangible assets	0	0
Pension asset	0	0
Other assets	0	0
Deferred income taxes	16	25
Total assets	8,571	8,103
Current liabilities
Accounts payable and accrued liabilities	53	54
Accounts payable, inter-company	2	0
Short-term advances from affiliates	3,226	3,253
Long-term debt maturing within one year	0	0
Total current liabilities	3,281	3,307
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	3,281	3,307
Shareholders’ equity
Share capital	2,065	2,058
Additional paid-in capital	48	43
Accumulated other comprehensive (loss) income	(1,481)	(1,477)
Retained earnings	4,658	4,172
Total Shareholders' equity	5,290	4,796
Total liabilities and shareholders’ equity	8,571	8,103
CPRC (Subsidiary Issuer) [Member]
Current assets
Cash and cash equivalents	376	502	153	152
Accounts receivable, net	470	452
Accounts receivable, inter-company	101	105
Short-term advances to affiliates	19	75
Materials and supplies	150	154
Other current assets	50	37
Total current assets	1,166	1,325
Long-term advances to affiliates	208	207
Investments	23	22
Investments in subsidiaries	9,657	9,832
Properties	8,456	8,481
Goodwill and intangible assets	0	3
Pension asset	1,489	1,401
Other assets	46	55
Deferred income taxes	0	0
Total assets	21,045	21,326
Current liabilities
Accounts payable and accrued liabilities	853	1,122
Accounts payable, inter-company	239	325
Short-term advances from affiliates	294	230
Long-term debt maturing within one year	23	24
Total current liabilities	1,409	1,701
Pension and other benefit liabilities	673	676
Long-term advances from affiliates	854	877
Other long-term liabilities	165	186
Long-term debt	8,369	8,863
Deferred income taxes	1,627	1,505
Total liabilities	13,097	13,808
Shareholders’ equity
Share capital	1,037	1,037
Additional paid-in capital	1,573	1,568
Accumulated other comprehensive (loss) income	(1,481)	(1,477)
Retained earnings	6,819	6,390
Total Shareholders' equity	7,948	7,518
Total liabilities and shareholders’ equity	21,045	21,326
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	195	148	CAD 31	CAD 74
Accounts receivable, net	159	193
Accounts receivable, inter-company	179	265
Short-term advances to affiliates	3,475	3,483
Materials and supplies	31	34
Other current assets	19	17
Total current assets	4,058	4,140
Long-term advances to affiliates	352	376
Investments	125	130
Investments in subsidiaries	0	0
Properties	7,557	7,792
Goodwill and intangible assets	196	208
Pension asset	0	0
Other assets	7	8
Deferred income taxes	0	0
Total assets	12,295	12,654
Current liabilities
Accounts payable and accrued liabilities	237	241
Accounts payable, inter-company	100	104
Short-term advances from affiliates	19	75
Long-term debt maturing within one year	0	6
Total current liabilities	356	426
Pension and other benefit liabilities	77	82
Long-term advances from affiliates	207	207
Other long-term liabilities	126	132
Long-term debt	61	64
Deferred income taxes	1,811	1,911
Total liabilities	2,638	2,822
Shareholders’ equity
Share capital	5,459	5,465
Additional paid-in capital	623	613
Accumulated other comprehensive (loss) income	569	840
Retained earnings	3,006	2,914
Total Shareholders' equity	9,657	9,832
Total liabilities and shareholders’ equity	CAD 12,295	CAD 12,654