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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive (income) loss for defined benefit plan, attributable to parent entity.

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Amount before tax, after reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss), attributable to parent entity.

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, on foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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Amount before tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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Condensed Consolidating Financial Information - Condensed Consolidating Statements of Comprehensive Income (Detail) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 984	CAD 510	CAD 480	CAD 431	CAD 384	CAD 347	CAD 328	CAD 540	CAD 2,405	CAD 1,599	CAD 1,352
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									24	18	(86)
Change in derivatives designated as cash flow hedges									19	(2)	(69)
Change in pension and post-retirement defined benefit plans									80	(434)	1,059
Other comprehensive income (loss) before income taxes									123	(418)	904
Income tax (expense) recovery on above items									(65)	96	(162)
Equity accounted investments									0	0	0
Other comprehensive income (loss)									58	(322)	742
Comprehensive income									2,463	1,277	2,094
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									(3,547)	(2,098)	(2,175)
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									0	0	0
Change in derivatives designated as cash flow hedges									0	0	0
Change in pension and post-retirement defined benefit plans									0	0	0
Other comprehensive income (loss) before income taxes									0	0	0
Income tax (expense) recovery on above items									0	0	0
Equity accounted investments									237	447	(1,412)
Other comprehensive income (loss)									237	447	(1,412)
Comprehensive income									(3,310)	(1,651)	(3,587)
CPRL (Parent Guarantor) [Member] \| Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									2,405	1,599	1,352
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									0	0	0
Change in derivatives designated as cash flow hedges									0	0	0
Change in pension and post-retirement defined benefit plans									0	0	0
Other comprehensive income (loss) before income taxes									0	0	0
Income tax (expense) recovery on above items									0	0	0
Equity accounted investments									58	(322)	742
Other comprehensive income (loss)									58	(322)	742
Comprehensive income									2,463	1,277	2,094
CPRC (Subsidiary Issuer) [Member] \| Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									2,367	1,566	1,410
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									318	149	(757)
Change in derivatives designated as cash flow hedges									19	(2)	(69)
Change in pension and post-retirement defined benefit plans									82	(443)	1,061
Other comprehensive income (loss) before income taxes									419	(296)	235
Income tax (expense) recovery on above items									(66)	99	(163)
Equity accounted investments									(295)	(125)	670
Other comprehensive income (loss)									58	(322)	742
Comprehensive income									2,425	1,244	2,152
Non-Guarantor Subsidiaries [Member] \| Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									1,180	532	765
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									(294)	(131)	671
Change in derivatives designated as cash flow hedges									0	0	0
Change in pension and post-retirement defined benefit plans									(2)	9	(2)
Other comprehensive income (loss) before income taxes									(296)	(122)	669
Income tax (expense) recovery on above items									1	(3)	1
Equity accounted investments									0	0	0
Other comprehensive income (loss)									(295)	(125)	670
Comprehensive income									CAD 885	CAD 407	CAD 1,435