Condensed Consolidating Financial Information - Condensed Consolidating Statements of Cash Flows (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	CAD 2,089	CAD 2,459	CAD 2,123
Investing activities
Additions to properties	(1,182)	(1,522)	(1,449)
Proceeds from sales of property, plant and equipment		281	236
Proceeds from sale of properties and other assets	116	114	52
Advances to affiliates	0	0	0
Repayment of advances to affiliates	0	0	0
Capital contributions to affiliates	0	0	0
Repurchase of share capital from affiliates	0	0
Other	(3)	4	0
Cash used in investing activities(1)	(1,069)	(1,123)	(1,161)
Financing activities
Dividends paid	(255)	(226)	(244)
Issuance of share capital	0	0	0
Return of share capital to affiliates	0	0
Issuance of CP Common Shares	21	43	62
Purchase of CP common shares	(1,210)	(2,787)	(2,050)
Proceeds from Issuance of Long-term Debt and Capital Securities, Net	0	3,411	0
Repayment of long-term debt, excluding commercial paper	(38)	(505)	(183)
Net repayment of commercial paper	(8)	(893)	771
Settlement of foreign exchange forward on long-term debt	0	0	17
Advances from affiliates	0	0	0
Repayment of advances from affiliates	0	0	0
Other	(3)	0	(3)
Cash used in financing activities	(1,493)	(957)	(1,630)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(13)	45	7
Cash position
(Decrease) increase in cash, cash equivalents, and restricted cash	(486)	424	(661)
Cash, cash equivalents, and restricted cash at beginning of year	650	226	887
Cash, cash equivalents, and restricted cash at end of year	164	650	226
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	(469)	(2,548)	(348)
Investing activities
Additions to properties	0	0	69
Proceeds from sales of property, plant and equipment		0	0
Proceeds from sale of properties and other assets	0	0	(69)
Advances to affiliates	1,203	3,264	3,247
Repayment of advances to affiliates	(222)	(1,804)	(3,759)
Capital contributions to affiliates	472	1,655	2,927
Repurchase of share capital from affiliates	(8)	(1,210)
Other	0	0	0
Cash used in investing activities(1)	1,445	1,905	2,415
Financing activities
Dividends paid	469	2,548	348
Issuance of share capital	(472)	(1,655)	(2,927)
Return of share capital to affiliates	8	1,210
Issuance of CP Common Shares	0	0	0
Purchase of CP common shares	0	0	0
Proceeds from Issuance of Long-term Debt and Capital Securities, Net		0
Repayment of long-term debt, excluding commercial paper	0	0	0
Net repayment of commercial paper	0	0	0
Settlement of foreign exchange forward on long-term debt			0
Advances from affiliates	(1,203)	(3,264)	(3,247)
Repayment of advances from affiliates	222	1,804	3,759
Other	0		0
Cash used in financing activities	(976)	643	(2,067)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0	0
Cash position
(Decrease) increase in cash, cash equivalents, and restricted cash	0	0	0
Cash, cash equivalents, and restricted cash at beginning of year	0	0	0
Cash, cash equivalents, and restricted cash at end of year	0	0	0
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	255	2,283	183
Investing activities
Additions to properties	0	0	0
Proceeds from sales of property, plant and equipment		0	0
Proceeds from sale of properties and other assets	0	0	0
Advances to affiliates	0	(1,133)	0
Repayment of advances to affiliates	0	0	0
Capital contributions to affiliates	0	0	0
Repurchase of share capital from affiliates	0	0
Other	0	0	0
Cash used in investing activities(1)	0	(1,133)	0
Financing activities
Dividends paid	(255)	(226)	(244)
Issuance of share capital	0	0	0
Return of share capital to affiliates	0	0
Issuance of CP Common Shares	21	43	62
Purchase of CP common shares	(1,210)	(2,787)	(2,050)
Proceeds from Issuance of Long-term Debt and Capital Securities, Net		0
Repayment of long-term debt, excluding commercial paper	0	0	0
Net repayment of commercial paper	0	0	0
Settlement of foreign exchange forward on long-term debt			0
Advances from affiliates	1,189	1,820	2,049
Repayment of advances from affiliates	0	0	0
Other	0		0
Cash used in financing activities	(255)	(1,150)	(183)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0	0
Cash position
(Decrease) increase in cash, cash equivalents, and restricted cash	0	0	0
Cash, cash equivalents, and restricted cash at beginning of year	0	0	0
Cash, cash equivalents, and restricted cash at end of year	0	0	0
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	1,424	1,650	1,684
Investing activities
Additions to properties	(728)	(766)	(816)
Proceeds from sales of property, plant and equipment		0	0
Proceeds from sale of properties and other assets	102	103	116
Advances to affiliates	(664)	(311)	(611)
Repayment of advances to affiliates	222	804	2,167
Capital contributions to affiliates	(472)	(1,655)	(2,927)
Repurchase of share capital from affiliates	8	1,210
Other	0	6	2
Cash used in investing activities(1)	(1,532)	(609)	(2,069)
Financing activities
Dividends paid	(255)	(2,272)	(182)
Issuance of share capital	0	0	0
Return of share capital to affiliates	0	0
Issuance of CP Common Shares	0	0	0
Purchase of CP common shares	0	0	0
Proceeds from Issuance of Long-term Debt and Capital Securities, Net		3,411
Repayment of long-term debt, excluding commercial paper	(24)	(461)	(174)
Net repayment of commercial paper	(8)	(893)	771
Settlement of foreign exchange forward on long-term debt			17
Advances from affiliates	0	500	1,198
Repayment of advances from affiliates	0	(1,000)	(1,592)
Other	(3)		0
Cash used in financing activities	(290)	(715)	38
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(4)	24	(3)
Cash position
(Decrease) increase in cash, cash equivalents, and restricted cash	(402)	350	(350)
Cash, cash equivalents, and restricted cash at beginning of year	502	152	502
Cash, cash equivalents, and restricted cash at end of year	100	502	152
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	879	1,074	604
Investing activities
Additions to properties	(454)	(756)	(702)
Proceeds from sales of property, plant and equipment		281	236
Proceeds from sale of properties and other assets	14	11	5
Advances to affiliates	(539)	(1,820)	(2,636)
Repayment of advances to affiliates	0	1,000	1,592
Capital contributions to affiliates	0	0	0
Repurchase of share capital from affiliates	0	0
Other	(3)	(2)	(2)
Cash used in investing activities(1)	(982)	(1,286)	(1,507)
Financing activities
Dividends paid	(214)	(276)	(166)
Issuance of share capital	472	1,655	2,927
Return of share capital to affiliates	(8)	(1,210)
Issuance of CP Common Shares	0	0	0
Purchase of CP common shares	0	0	0
Proceeds from Issuance of Long-term Debt and Capital Securities, Net		0
Repayment of long-term debt, excluding commercial paper	(14)	(44)	(9)
Net repayment of commercial paper	0	0	0
Settlement of foreign exchange forward on long-term debt			0
Advances from affiliates	14	944	0
Repayment of advances from affiliates	(222)	(804)	(2,167)
Other	0		(3)
Cash used in financing activities	28	265	582
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	(9)	21	10
Cash position
(Decrease) increase in cash, cash equivalents, and restricted cash	(84)	74	(311)
Cash, cash equivalents, and restricted cash at beginning of year	148	74	385
Cash, cash equivalents, and restricted cash at end of year	CAD 64	CAD 148	CAD 74