Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Cash Flows (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	$ 397	$ 311
Investing activities
Additions to properties	(241)	(230)
Proceeds from sale of properties and other assets	4	3
Advances to affiliates	0	0
Repayment of advances to affiliates	0
Capital contributions to affiliates		0
Repurchase of share capital from affiliates	0
Other	(1)	5
Cash used in investing activities	(238)	(222)
Financing activities
Dividends paid	(82)	(73)
Issuance of share capital		0
Return of share capital to affiliates	0
Issuance of CP Common Shares	8	28
Purchase of CP Common Shares	(298)	0
Repayment of long-term debt, excluding commercial paper	(5)	(5)
Advances from affiliates	0	0
Repayments of advances from affiliates	0
Cash used in financing activities	(377)	(50)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	5	(2)
Cash position
Increase (decrease) in cash and cash equivalents	(213)	37
Cash and cash equivalents at beginning of period	338	164
Cash and cash equivalents at end of period	125	201
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	(195)	(101)
Investing activities
Additions to properties	0	0
Proceeds from sale of properties and other assets	0	0
Advances to affiliates	307	286
Repayment of advances to affiliates	(502)
Capital contributions to affiliates		68
Repurchase of share capital from affiliates	(423)
Other	0	0
Cash used in investing activities	(618)	354
Financing activities
Dividends paid	195	101
Issuance of share capital		(68)
Return of share capital to affiliates	423
Issuance of CP Common Shares	0	0
Purchase of CP Common Shares	0
Repayment of long-term debt, excluding commercial paper	0	0
Advances from affiliates	(307)	(286)
Repayments of advances from affiliates	502
Cash used in financing activities	813	(253)
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0
Cash position
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	65	63
Investing activities
Additions to properties	0	0
Proceeds from sale of properties and other assets	0	0
Advances to affiliates	0	(152)
Repayment of advances to affiliates	0
Capital contributions to affiliates		0
Repurchase of share capital from affiliates	0
Other	0	0
Cash used in investing activities	0	(152)
Financing activities
Dividends paid	(82)	(73)
Issuance of share capital		0
Return of share capital to affiliates	0
Issuance of CP Common Shares	8	28
Purchase of CP Common Shares	(298)
Repayment of long-term debt, excluding commercial paper	0	0
Advances from affiliates	307	134
Repayments of advances from affiliates	0
Cash used in financing activities	(65)	89
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	0	0
Cash position
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	392	85
Investing activities
Additions to properties	(122)	(109)
Proceeds from sale of properties and other assets	3	1
Advances to affiliates	(307)	0
Repayment of advances to affiliates	0
Capital contributions to affiliates		(68)
Repurchase of share capital from affiliates	423
Other	0	5
Cash used in investing activities	(3)	(171)
Financing activities
Dividends paid	(82)	(73)
Issuance of share capital		0
Return of share capital to affiliates	0
Issuance of CP Common Shares	0	0
Purchase of CP Common Shares	0
Repayment of long-term debt, excluding commercial paper	(5)	(5)
Advances from affiliates	0	149
Repayments of advances from affiliates	(502)
Cash used in financing activities	(589)	71
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	2	(2)
Cash position
Increase (decrease) in cash and cash equivalents	(198)	(17)
Cash and cash equivalents at beginning of period	241	100
Cash and cash equivalents at end of period	43	83
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Cash provided by operating activities	135	264
Investing activities
Additions to properties	(119)	(121)
Proceeds from sale of properties and other assets	1	2
Advances to affiliates	0	(134)
Repayment of advances to affiliates	502
Capital contributions to affiliates		0
Repurchase of share capital from affiliates	0
Other	(1)	0
Cash used in investing activities	383	(253)
Financing activities
Dividends paid	(113)	(28)
Issuance of share capital		68
Return of share capital to affiliates	(423)
Issuance of CP Common Shares	0	0
Purchase of CP Common Shares	0
Repayment of long-term debt, excluding commercial paper	0	0
Advances from affiliates	0	3
Repayments of advances from affiliates	0
Cash used in financing activities	(536)	43
Effect of foreign currency fluctuations on U.S. dollar-denominated cash and cash equivalents	3	0
Cash position
Increase (decrease) in cash and cash equivalents	(15)	54
Cash and cash equivalents at beginning of period	97	64
Cash and cash equivalents at end of period	$ 82	$ 118