Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Cash Flows (Details) - CAD CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	CAD 611	CAD 512	CAD 922	CAD 730
Investing activities
Additions to properties	(346)	(330)	(576)	(608)
Proceeds from sale of properties and other assets	13	11	16	71
Advances to affiliates	0	0	0	0
Repayment of advances to affiliates	0	0		0
Capital contributions to affiliates	0	0	0	0
Repurchase of share capital from affiliates				0
Other	0	(2)	5	(2)
Cash used in investing activities	(333)	(321)	(555)	(539)
Financing activities
Dividends paid	(73)	(53)	(146)	(107)
Return of share capital to affiliates				0
Issuance of share capital	0	0	0	0
Issuance of CP Common Shares	9	4	37	9
Purchase of CP Common Shares	(142)	(788)	(142)	(788)
Repayment of long-term debt, excluding commercial paper	(9)	(7)	(14)	(18)
Net issuance (repayment) of commercial paper	0	176	0	176
Advances from affiliates	0	0	0	0
Repayment of advances from affiliates	0	0		0
Settlement of forward starting swaps	(22)	0	(22)	0
Other	0	(1)	0	(3)
Cash used in financing activities	(237)	(669)	(287)	(731)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(4)	(1)	(6)	(18)
Cash position
Increase (decrease) in cash and cash equivalents	37	(479)	74	(558)
Cash and cash equivalents at beginning of period	201	571	164	650
Cash and cash equivalents at end of period	238	92	238	92
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	(191)	(156)	(292)	(210)
Investing activities
Additions to properties	0	0	0	0
Proceeds from sale of properties and other assets	0	0	0	0
Advances to affiliates	2,612	767	2,896	802
Repayment of advances to affiliates	(2)	(208)		(208)
Capital contributions to affiliates	945	348	1,013	357
Repurchase of share capital from affiliates				(6)
Other	0	0	0	0
Cash used in investing activities	3,555	907	3,909	945
Financing activities
Dividends paid	191	156	292	210
Return of share capital to affiliates				6
Issuance of share capital	(945)	(348)	(1,013)	(357)
Issuance of CP Common Shares	0	0	0	0
Purchase of CP Common Shares	0	0	0	0
Repayment of long-term debt, excluding commercial paper	0	0	0	0
Net issuance (repayment) of commercial paper		0		0
Advances from affiliates	(2,612)	(767)	(2,896)	(802)
Repayment of advances from affiliates	2	208		208
Settlement of forward starting swaps	0		0
Other		0		0
Cash used in financing activities	(3,364)	(751)	(3,617)	(735)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0	0	0
Cash position
Increase (decrease) in cash and cash equivalents	0	0	0	0
Cash and cash equivalents at beginning of period	0	0	0	0
Cash and cash equivalents at end of period	0	0	0	0
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	95	75	158	98
Investing activities
Additions to properties	0	0	0	0
Proceeds from sale of properties and other assets	0	0	0	0
Advances to affiliates	(1,086)	0	(1,238)	0
Repayment of advances to affiliates	0	0		0
Capital contributions to affiliates	0	0	0	0
Repurchase of share capital from affiliates				0
Other	0	0	0	0
Cash used in investing activities	(1,086)	0	(1,238)	0
Financing activities
Dividends paid	(73)	(53)	(146)	(107)
Return of share capital to affiliates				0
Issuance of share capital	0	0	0	0
Issuance of CP Common Shares	9	4	37	9
Purchase of CP Common Shares	(142)	(788)	(142)	(788)
Repayment of long-term debt, excluding commercial paper	0	0	0	0
Net issuance (repayment) of commercial paper		0		0
Advances from affiliates	1,197	762	1,331	788
Repayment of advances from affiliates	0	0		0
Settlement of forward starting swaps	0		0
Other		0		0
Cash used in financing activities	991	(75)	1,080	(98)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0	0	0
Cash position
Increase (decrease) in cash and cash equivalents	0	0	0	0
Cash and cash equivalents at beginning of period	0	0	0	0
Cash and cash equivalents at end of period	0	0	0	0
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	468	374	553	425
Investing activities
Additions to properties	(192)	(206)	(301)	(338)
Proceeds from sale of properties and other assets	5	11	6	68
Advances to affiliates	(553)	(482)	(551)	(517)
Repayment of advances to affiliates	2	208		208
Capital contributions to affiliates	(945)	(348)	(1,013)	(357)
Repurchase of share capital from affiliates				6
Other	1	0	6	0
Cash used in investing activities	(1,682)	(817)	(1,853)	(930)
Financing activities
Dividends paid	(73)	(53)	(146)	(107)
Return of share capital to affiliates				0
Issuance of share capital	0	0	0	0
Issuance of CP Common Shares	0	0	0	0
Purchase of CP Common Shares	0	0	0	0
Repayment of long-term debt, excluding commercial paper	(9)	(7)	(14)	(11)
Net issuance (repayment) of commercial paper		176		176
Advances from affiliates	1,415	0	1,564	0
Repayment of advances from affiliates	0	0		0
Settlement of forward starting swaps	(22)		(22)
Other		(1)		(3)
Cash used in financing activities	1,311	115	1,382	55
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(2)	(1)	(4)	(5)
Cash position
Increase (decrease) in cash and cash equivalents	95	(329)	78	(455)
Cash and cash equivalents at beginning of period	83	376	100	502
Cash and cash equivalents at end of period	178	47	178	47
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	239	219	503	417
Investing activities
Additions to properties	(154)	(124)	(275)	(270)
Proceeds from sale of properties and other assets	8	0	10	3
Advances to affiliates	(973)	(285)	(1,107)	(285)
Repayment of advances to affiliates	0	0		0
Capital contributions to affiliates	0	0	0	0
Repurchase of share capital from affiliates				0
Other	(1)	(2)	(1)	(2)
Cash used in investing activities	(1,120)	(411)	(1,373)	(554)
Financing activities
Dividends paid	(118)	(103)	(146)	(103)
Return of share capital to affiliates				(6)
Issuance of share capital	945	348	1,013	357
Issuance of CP Common Shares	0	0	0	0
Purchase of CP Common Shares	0	0	0	0
Repayment of long-term debt, excluding commercial paper	0	0	0	(7)
Net issuance (repayment) of commercial paper		0		0
Advances from affiliates	0	5	1	14
Repayment of advances from affiliates	(2)	(208)		(208)
Settlement of forward starting swaps	0		0
Other		0		0
Cash used in financing activities	825	42	868	47
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(2)	0	(2)	(13)
Cash position
Increase (decrease) in cash and cash equivalents	(58)	(150)	(4)	(103)
Cash and cash equivalents at beginning of period	118	195	64	148
Cash and cash equivalents at end of period	CAD 60	CAD 45	CAD 60	CAD 45