Condensed Consolidating Financial Information - Condensed Consolidating Statements of Comprehensive Income (Detail) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 319	CAD 323	CAD 390	CAD 320	CAD 451	CAD 400	CAD 371	CAD 254	CAD 1,352	CAD 1,476	CAD 875
Net (loss) gain in foreign currency translation adjustments, net of hedging activities									(86)	(32)	3
Change in derivatives designated as cash flow hedges									(69)	(49)	(1)
Change in pension and post-retirement defined benefit plans									1,059	(941)	1,681
Other comprehensive (loss) income before income taxes									904	(1,022)	1,683
Income tax (expense) recovery on above items									(162)	306	(418)
Equity accounted investments									0	0	0
Other comprehensive (loss) income									742	(716)	1,265
Comprehensive income									2,094	760	2,140
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									(2,175)	(2,037)	(1,056)
Net (loss) gain 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 (loss) income before income taxes									0	0	0
Income tax (expense) recovery on above items									0	0	0
Equity accounted investments									(1,412)	452	(1,519)
Other comprehensive (loss) income									(1,412)	452	(1,519)
Comprehensive income									(3,587)	(1,585)	(2,575)
CPRL (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									1,352	1,476	875
Net (loss) gain 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 (loss) income before income taxes									0	0	0
Income tax (expense) recovery on above items									0	0	0
Equity accounted investments									742	(716)	1,265
Other comprehensive (loss) income									742	(716)	1,265
Comprehensive income									2,094	760	2,140
CPRC (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									1,410	1,478	875
Net (loss) gain in foreign currency translation adjustments, net of hedging activities									(757)	(316)	(219)
Change in derivatives designated as cash flow hedges									(69)	(49)	(1)
Change in pension and post-retirement defined benefit plans									1,061	(908)	1,631
Other comprehensive (loss) income before income taxes									235	(1,273)	1,411
Income tax (expense) recovery on above items									(163)	293	(400)
Equity accounted investments									670	264	254
Other comprehensive (loss) income									742	(716)	1,265
Comprehensive income									2,152	762	2,140
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									765	559	181
Net (loss) gain in foreign currency translation adjustments, net of hedging activities									671	284	222
Change in derivatives designated as cash flow hedges									0	0	0
Change in pension and post-retirement defined benefit plans									(2)	(33)	50
Other comprehensive (loss) income before income taxes									669	251	272
Income tax (expense) recovery on above items									1	13	(18)
Equity accounted investments									0	0	0
Other comprehensive (loss) income									670	264	254
Comprehensive income									CAD 1,435	CAD 823	CAD 435