Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Net income	$ 724	$ 436	$ 1,158	$ 784
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	15	(16)	31	(36)
Change in derivatives designated as cash flow hedges	4	14	6	35
Change in pension and post-retirement defined benefit plans	21	29	41	58
Other comprehensive income before income taxes	40	27	78	57
Income tax recovery (expense) on above items	(22)	5	(44)	11
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	18	32	34	68
Comprehensive income	742	468	1,192	852
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(978)	(645)	(1,530)	(1,152)
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	0	0	0	0
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	0	0	0	0
Other comprehensive income before income taxes	0	0	0	0
Income tax recovery (expense) on above items	0	0	0	0
Equity accounted investments	87	(140)	174	(307)
Other comprehensive income (loss)	87	(140)	174	(307)
Comprehensive income	(891)	(785)	(1,356)	(1,459)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	724	436	1,158	784
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	0	0	0	0
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	0	0	0	0
Other comprehensive income before income taxes	0	0	0	0
Income tax recovery (expense) on above items	0	0	0	0
Equity accounted investments	18	32	34	68
Other comprehensive income (loss)	18	32	34	68
Comprehensive income	742	468	1,192	852
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	720	438	1,148	800
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	121	(123)	241	(273)
Change in derivatives designated as cash flow hedges	4	14	6	35
Change in pension and post-retirement defined benefit plans	20	27	39	55
Other comprehensive income before income taxes	145	(82)	286	(183)
Income tax recovery (expense) on above items	(22)	6	(44)	12
Equity accounted investments	(105)	108	(208)	239
Other comprehensive income (loss)	18	32	34	68
Comprehensive income	738	470	1,182	868
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	258	207	382	352
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(106)	107	(210)	237
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	1	2	2	3
Other comprehensive income before income taxes	(105)	109	(208)	240
Income tax recovery (expense) on above items	0	(1)	0	(1)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	(105)	108	(208)	239
Comprehensive income	$ 153	$ 315	$ 174	$ 591