Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	CAD 92	CAD 571	CAD 650	CAD 185	CAD 184	CAD 226
Accounts receivable, net	577		645
Accounts receivable, inter-company	0		0
Short-term advances to affiliates	0		0
Materials and supplies	195		188
Other current assets	59		54
Total current assets	923		1,537
Long-term advances to affiliates	0		0
Investments	155		152
Investments in subsidiaries	0		0
Properties	16,160		16,273
Goodwill and intangible assets	195		211
Pension asset	1,565		1,401
Other assets	70		63
Deferred income taxes	0		0
Total assets	19,068		19,637
Current liabilities
Accounts payable and accrued liabilities	1,247		1,417
Accounts payable, inter-company	0		0
Short-term advances from affiliates	0		0
Long-term debt maturing within one year	198		30
Total current liabilities	1,445		1,447
Pension and other benefit liabilities	751		758
Long-term advances from affiliates	0		0
Other long-term liabilities	286		318
Long-term debt	8,383		8,927
Deferred income taxes	3,512		3,391
Total liabilities	14,377		14,841
Shareholders’ equity
Share capital	2,000		2,058
Additional paid-in capital	49		43
Accumulated other comprehensive (loss) income	(1,471)		(1,477)
Retained earnings	4,113		4,172
Total Shareholders' equity	4,691		4,796	5,251		5,610
Total liabilities and shareholders’ equity	19,068		19,637
Consolidating Adjustments and Eliminations [Member]
Current assets
Cash and cash equivalents	0	0	0	0	0	0
Accounts receivable, net	0		0
Accounts receivable, inter-company	(317)		(429)
Short-term advances to affiliates	(4,228)		(3,558)
Materials and supplies	0		0
Other current assets	0		0
Total current assets	(4,545)		(3,987)
Long-term advances to affiliates	(589)		(1,084)
Investments	0		0
Investments in subsidiaries	(17,970)		(17,350)
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	(14)		(25)
Total assets	(23,118)		(22,446)
Current liabilities
Accounts payable and accrued liabilities	0		0
Accounts payable, inter-company	(317)		(429)
Short-term advances from affiliates	(4,228)		(3,558)
Long-term debt maturing within one year	0		0
Total current liabilities	(4,545)		(3,987)
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	(589)		(1,084)
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	(14)		(25)
Total liabilities	(5,148)		(5,096)
Shareholders’ equity
Share capital	(6,845)		(6,502)
Additional paid-in capital	(2,048)		(2,181)
Accumulated other comprehensive (loss) income	923		637
Retained earnings	(10,000)		(9,304)
Total Shareholders' equity	(17,970)		(17,350)
Total liabilities and shareholders’ equity	(23,118)		(22,446)
CPRL (Parent Guarantor) [Member]
Current assets
Cash and cash equivalents	0	0	0	0	0	0
Accounts receivable, net	0		0
Accounts receivable, inter-company	78		59
Short-term advances to affiliates	0		0
Materials and supplies	0		0
Other current assets	0		0
Total current assets	78		59
Long-term advances to affiliates	501		501
Investments	0		0
Investments in subsidiaries	8,217		7,518
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	14		25
Total assets	8,810		8,103
Current liabilities
Accounts payable and accrued liabilities	156		54
Accounts payable, inter-company	3		0
Short-term advances from affiliates	3,960		3,253
Long-term debt maturing within one year	0		0
Total current liabilities	4,119		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	4,119		3,307
Shareholders’ equity
Share capital	2,000		2,058
Additional paid-in capital	49		43
Accumulated other comprehensive (loss) income	(1,471)		(1,477)
Retained earnings	4,113		4,172
Total Shareholders' equity	4,691		4,796
Total liabilities and shareholders’ equity	8,810		8,103
CPRC (Subsidiary Issuer) [Member]
Current assets
Cash and cash equivalents	47	376	502	139	153	152
Accounts receivable, net	406		452
Accounts receivable, inter-company	80		105
Short-term advances to affiliates	470		75
Materials and supplies	164		154
Other current assets	49		37
Total current assets	1,216		1,325
Long-term advances to affiliates	0		207
Investments	26		22
Investments in subsidiaries	9,753		9,832
Properties	8,560		8,481
Goodwill and intangible assets	0		3
Pension asset	1,565		1,401
Other assets	50		55
Deferred income taxes	0		0
Total assets	21,170		21,326
Current liabilities
Accounts payable and accrued liabilities	804		1,122
Accounts payable, inter-company	235		325
Short-term advances from affiliates	247		230
Long-term debt maturing within one year	198		24
Total current liabilities	1,484		1,701
Pension and other benefit liabilities	675		676
Long-term advances from affiliates	589		877
Other long-term liabilities	159		186
Long-term debt	8,323		8,863
Deferred income taxes	1,723		1,505
Total liabilities	12,953		13,808
Shareholders’ equity
Share capital	1,037		1,037
Additional paid-in capital	1,630		1,568
Accumulated other comprehensive (loss) income	(1,471)		(1,477)
Retained earnings	7,021		6,390
Total Shareholders' equity	8,217		7,518
Total liabilities and shareholders’ equity	21,170		21,326
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	45	CAD 195	148	CAD 46	CAD 31	CAD 74
Accounts receivable, net	171		193
Accounts receivable, inter-company	159		265
Short-term advances to affiliates	3,758		3,483
Materials and supplies	31		34
Other current assets	10		17
Total current assets	4,174		4,140
Long-term advances to affiliates	88		376
Investments	129		130
Investments in subsidiaries	0		0
Properties	7,600		7,792
Goodwill and intangible assets	195		208
Pension asset	0		0
Other assets	20		8
Deferred income taxes	0		0
Total assets	12,206		12,654
Current liabilities
Accounts payable and accrued liabilities	287		241
Accounts payable, inter-company	79		104
Short-term advances from affiliates	21		75
Long-term debt maturing within one year	0		6
Total current liabilities	387		426
Pension and other benefit liabilities	76		82
Long-term advances from affiliates	0		207
Other long-term liabilities	127		132
Long-term debt	60		64
Deferred income taxes	1,803		1,911
Total liabilities	2,453		2,822
Shareholders’ equity
Share capital	5,808		5,465
Additional paid-in capital	418		613
Accumulated other comprehensive (loss) income	548		840
Retained earnings	2,979		2,914
Total Shareholders' equity	9,753		9,832
Total liabilities and shareholders’ equity	CAD 12,206		CAD 12,654