Condensed Consolidating Financial Information - Condensed Consolidating Statements of Comprehensive Income (Detail) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 384	CAD 347	CAD 328	CAD 540	CAD 319	CAD 323	CAD 390	CAD 320	CAD 1,599	CAD 1,352	CAD 1,476
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									18	(86)	(32)
Change in derivatives designated as cash flow hedges									(2)	(69)	(49)
Change in pension and post-retirement defined benefit plans									(434)	1,059	(941)
Other comprehensive income before income taxes									(418)	904	(1,022)
Income tax recovery (expense) on above items									96	(162)	306
Equity accounted investments									0	0	0
Other comprehensive income									(322)	742	(716)
Comprehensive income									1,277	2,094	760
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									(2,098)	(2,175)	(2,037)
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 before income taxes									0	0	0
Income tax recovery (expense) on above items									0	0	0
Equity accounted investments									447	(1,412)	452
Other comprehensive income									447	(1,412)	452
Comprehensive income									(1,651)	(3,587)	(1,585)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									1,599	1,352	1,476
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 before income taxes									0	0	0
Income tax recovery (expense) on above items									0	0	0
Equity accounted investments									(322)	742	(716)
Other comprehensive income									(322)	742	(716)
Comprehensive income									1,277	2,094	760
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									1,566	1,410	1,478
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									149	(757)	(316)
Change in derivatives designated as cash flow hedges									(2)	(69)	(49)
Change in pension and post-retirement defined benefit plans									(443)	1,061	(908)
Other comprehensive income before income taxes									(296)	235	(1,273)
Income tax recovery (expense) on above items									99	(163)	293
Equity accounted investments									(125)	670	264
Other comprehensive income									(322)	742	(716)
Comprehensive income									1,244	2,152	762
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									532	765	559
Net gain (loss) in foreign currency translation adjustments, net of hedging activities									(131)	671	284
Change in derivatives designated as cash flow hedges									0	0	0
Change in pension and post-retirement defined benefit plans									9	(2)	(33)
Other comprehensive income before income taxes									(122)	669	251
Income tax recovery (expense) on above items									(3)	1	13
Equity accounted investments									0	0	0
Other comprehensive income									(125)	670	264
Comprehensive income									CAD 407	CAD 1,435	CAD 823