Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Cash Flows (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	CAD 527	CAD 591	CAD 1,449	CAD 1,321
Investing activities
Additions to properties	(319)	(294)	(895)	(902)
Proceeds from sale of properties and other assets	13	16	29	87
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		0	0
Other	0	0	5	(2)
Cash used in investing activities	(306)	(278)	(861)	(817)
Financing activities
Dividends paid	(83)	(75)	(229)	(182)
Return of share capital to affiliates	0		0	0
Issuance of share capital	0	0	0	0
Issuance of CP Common Shares	2	5	39	14
Purchase of CP Common Shares	(226)	(412)	(368)	(1,200)
Repayment of long-term debt, excluding commercial paper	(3)	(12)	(17)	(30)
Net issuance (repayment) of commercial paper	0	190	0	366
Advances from affiliates	0	0	0	0
Settlement of forward starting swaps	0	0	(22)	0
Repayments of advances from affiliates	0	0		0
Other	0	0	0	(3)
Cash used in financing activities	(310)	(304)	(597)	(1,035)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(7)	2	(13)	(16)
Cash position
Increase (decrease) in cash and cash equivalents	(96)	11	(22)	(547)
Cash and cash equivalents at beginning of period	238	92	164	650
Cash and cash equivalents at end of period	142	103	142	103
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	(106)	(128)	(398)	(338)
Investing activities
Additions to properties	0	0	0	0
Proceeds from sale of properties and other assets	0	0	0	0
Advances to affiliates	50	398	2,786	1,200
Repayment of advances to affiliates	(160)	(14)		(222)
Capital contributions to affiliates	26	46	1,039	403
Repurchase of share capital from affiliates	(32)		(32)	(6)
Other			0	0
Cash used in investing activities	(116)	430	3,793	1,375
Financing activities
Dividends paid	106	128	398	338
Return of share capital to affiliates	32		32	6
Issuance of share capital	(26)	(46)	(1,039)	(403)
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	(50)	(398)	(2,786)	(1,200)
Settlement of forward starting swaps			0
Repayments of advances from affiliates	160	14		222
Other				0
Cash used in financing activities	222	(302)	(3,395)	(1,037)
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	98	84	256	182
Investing activities
Additions to properties	0	0	0	0
Proceeds from sale of properties and other assets	0	0	0	0
Advances to affiliates	0	0	(1,079)	0
Repayment of advances to affiliates	159	0		0
Capital contributions to affiliates	0	0	0	0
Repurchase of share capital from affiliates	0		0	0
Other			0	0
Cash used in investing activities	159	0	(1,079)	0
Financing activities
Dividends paid	(83)	(75)	(229)	(182)
Return of share capital to affiliates	0		0	0
Issuance of share capital	0	0	0	0
Issuance of CP Common Shares	2	5	39	14
Purchase of CP Common Shares	(226)	(412)	(368)	(1,200)
Repayment of long-term debt, excluding commercial paper	0	0	0	0
Net issuance (repayment) of commercial paper		0		0
Advances from affiliates	50	398	1,381	1,186
Settlement of forward starting swaps			0
Repayments of advances from affiliates	0	0		0
Other				0
Cash used in financing activities	(257)	(84)	823	(182)
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	322	406	875	831
Investing activities
Additions to properties	(193)	(238)	(494)	(576)
Proceeds from sale of properties and other assets	11	6	17	74
Advances to affiliates	0	(275)	(550)	(792)
Repayment of advances to affiliates	1	14		222
Capital contributions to affiliates	(26)	(46)	(1,039)	(403)
Repurchase of share capital from affiliates	32		32	6
Other			6	0
Cash used in investing activities	(175)	(539)	(2,028)	(1,469)
Financing activities
Dividends paid	(83)	(75)	(229)	(182)
Return of share capital to affiliates	0		0	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	(3)	(5)	(17)	(16)
Net issuance (repayment) of commercial paper		190		366
Advances from affiliates	0	0	1,405	0
Settlement of forward starting swaps			(22)
Repayments of advances from affiliates	(159)	0		0
Other				(3)
Cash used in financing activities	(245)	110	1,137	165
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(2)	0	(6)	(5)
Cash position
Increase (decrease) in cash and cash equivalents	(100)	(23)	(22)	(478)
Cash and cash equivalents at beginning of period	178	47	100	502
Cash and cash equivalents at end of period	78	24	78	24
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	213	229	716	646
Investing activities
Additions to properties	(126)	(56)	(401)	(326)
Proceeds from sale of properties and other assets	2	10	12	13
Advances to affiliates	(50)	(123)	(1,157)	(408)
Repayment of advances to affiliates	0	0		0
Capital contributions to affiliates	0	0	0	0
Repurchase of share capital from affiliates	0		0	0
Other			(1)	(2)
Cash used in investing activities	(174)	(169)	(1,547)	(723)
Financing activities
Dividends paid	(23)	(53)	(169)	(156)
Return of share capital to affiliates	(32)		(32)	(6)
Issuance of share capital	26	46	1,039	403
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	(7)	0	(14)
Net issuance (repayment) of commercial paper		0		0
Advances from affiliates	0	0	0	14
Settlement of forward starting swaps			0
Repayments of advances from affiliates	(1)	(14)		(222)
Other				0
Cash used in financing activities	(30)	(28)	838	19
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(5)	2	(7)	(11)
Cash position
Increase (decrease) in cash and cash equivalents	4	34	0	(69)
Cash and cash equivalents at beginning of period	60	45	64	148
Cash and cash equivalents at end of period	CAD 64	CAD 79	CAD 64	CAD 79