Condensed Consolidating Financial Information - Interim Condensed Consolidating Balance Sheets (Details) - CAD CAD in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	CAD 103	CAD 92	CAD 650	CAD 661	CAD 185	CAD 226
Accounts receivable, net	605		645
Accounts receivable, inter-company	0		0
Short-term advances to affiliates	0		0
Materials and supplies	192		188
Other current assets	64		54
Total current assets	964		1,537
Long-term advances to affiliates	0		0
Investments	169		152
Investments in subsidiaries	0		0
Properties	16,382		16,273
Goodwill and intangible assets	198		211
Pension asset	1,638		1,401
Other assets	70		63
Deferred income taxes	0		0
Total assets	19,421		19,637
Current liabilities
Accounts payable and accrued liabilities	1,246		1,417
Accounts payable, inter-company	0		0
Short-term advances from affiliates	0		0
Long-term debt maturing within one year	391		30
Total current liabilities	1,637		1,447
Pension and other benefit liabilities	756		758
Long-term advances from affiliates	0		0
Other long-term liabilities	280		318
Long-term debt	8,488		8,927
Deferred income taxes	3,591		3,391
Total liabilities	14,752		14,841
Shareholders’ equity
Share capital	2,000		2,058
Additional paid-in capital	43		43
Accumulated other comprehensive (loss) income	(1,433)		(1,477)
Retained earnings	4,059		4,172
Total Shareholders' equity	4,669		4,796	3,992		5,610
Total liabilities and shareholders’ equity	19,421		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	(357)		(429)
Short-term advances to affiliates	(5,190)		(3,558)
Materials and supplies	0		0
Other current assets	0		0
Total current assets	(5,547)		(3,987)
Long-term advances to affiliates	(91)		(1,084)
Investments	0		0
Investments in subsidiaries	(18,520)		(17,350)
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	0		0
Deferred income taxes	(5)		(25)
Total assets	(24,163)		(22,446)
Current liabilities
Accounts payable and accrued liabilities	0		0
Accounts payable, inter-company	(357)		(429)
Short-term advances from affiliates	(5,190)		(3,558)
Long-term debt maturing within one year	0		0
Total current liabilities	(5,547)		(3,987)
Pension and other benefit liabilities	0		0
Long-term advances from affiliates	(91)		(1,084)
Other long-term liabilities	0		0
Long-term debt	0		0
Deferred income taxes	(5)		(25)
Total liabilities	(5,643)		(5,096)
Shareholders’ equity
Share capital	(6,891)		(6,502)
Additional paid-in capital	(2,053)		(2,181)
Accumulated other comprehensive (loss) income	821		637
Retained earnings	(10,397)		(9,304)
Total Shareholders' equity	(18,520)		(17,350)
Total liabilities and shareholders’ equity	(24,163)		(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	88		59
Short-term advances to affiliates	500		0
Materials and supplies	0		0
Other current assets	0		0
Total current assets	588		59
Long-term advances to affiliates	0		501
Investments	0		0
Investments in subsidiaries	8,547		7,518
Properties	0		0
Goodwill and intangible assets	0		0
Pension asset	0		0
Other assets	1		0
Deferred income taxes	5		25
Total assets	9,141		8,103
Current liabilities
Accounts payable and accrued liabilities	84		54
Accounts payable, inter-company	14		0
Short-term advances from affiliates	4,373		3,253
Long-term debt maturing within one year	0		0
Total current liabilities	4,471		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	1		0
Total liabilities	4,472		3,307
Shareholders’ equity
Share capital	2,000		2,058
Additional paid-in capital	43		43
Accumulated other comprehensive (loss) income	(1,433)		(1,477)
Retained earnings	4,059		4,172
Total Shareholders' equity	4,669		4,796
Total liabilities and shareholders’ equity	9,141		8,103
CPRC (Subsidiary Issuer) [Member]
Current assets
Cash and cash equivalents	24	47	502	354	139	152
Accounts receivable, net	435		452
Accounts receivable, inter-company	106		105
Short-term advances to affiliates	798		75
Materials and supplies	160		154
Other current assets	42		37
Total current assets	1,565		1,325
Long-term advances to affiliates	0		207
Investments	28		22
Investments in subsidiaries	9,973		9,832
Properties	8,695		8,481
Goodwill and intangible assets	0		3
Pension asset	1,638		1,401
Other assets	51		55
Deferred income taxes	0		0
Total assets	21,950		21,326
Current liabilities
Accounts payable and accrued liabilities	880		1,122
Accounts payable, inter-company	247		325
Short-term advances from affiliates	808		230
Long-term debt maturing within one year	391		24
Total current liabilities	2,326		1,701
Pension and other benefit liabilities	680		676
Long-term advances from affiliates	91		877
Other long-term liabilities	149		186
Long-term debt	8,434		8,863
Deferred income taxes	1,723		1,505
Total liabilities	13,403		13,808
Shareholders’ equity
Share capital	1,037		1,037
Additional paid-in capital	1,634		1,568
Accumulated other comprehensive (loss) income	(1,433)		(1,477)
Retained earnings	7,309		6,390
Total Shareholders' equity	8,547		7,518
Total liabilities and shareholders’ equity	21,950		21,326
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	79	CAD 45	148	CAD 307	CAD 46	CAD 74
Accounts receivable, net	170		193
Accounts receivable, inter-company	163		265
Short-term advances to affiliates	3,892		3,483
Materials and supplies	32		34
Other current assets	22		17
Total current assets	4,358		4,140
Long-term advances to affiliates	91		376
Investments	141		130
Investments in subsidiaries	0		0
Properties	7,687		7,792
Goodwill and intangible assets	198		208
Pension asset	0		0
Other assets	18		8
Deferred income taxes	0		0
Total assets	12,493		12,654
Current liabilities
Accounts payable and accrued liabilities	282		241
Accounts payable, inter-company	96		104
Short-term advances from affiliates	9		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	131		132
Long-term debt	54		64
Deferred income taxes	1,872		1,911
Total liabilities	2,520		2,822
Shareholders’ equity
Share capital	5,854		5,465
Additional paid-in capital	419		613
Accumulated other comprehensive (loss) income	612		840
Retained earnings	3,088		2,914
Total Shareholders' equity	9,973		9,832
Total liabilities and shareholders’ equity	CAD 12,493		CAD 12,654