Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Net income	$ 618	$ 622	$ 1,776	$ 1,406
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(8)	12	23	(24)
Change in derivatives designated as cash flow hedges	2	1	8	36
Change in pension and post-retirement defined benefit plans	20	28	61	86
Other comprehensive income before income taxes	14	41	92	98
Income tax recovery (expense) on above items	3	(22)	(41)	(11)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	17	19	51	87
Comprehensive income	635	641	1,827	1,493
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(808)	(815)	(2,338)	(1,967)
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	(78)	64	96	(243)
Other comprehensive income (loss)	(78)	64	96	(243)
Comprehensive income	(886)	(751)	(2,242)	(2,210)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	618	622	1,776	1,406
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	17	19	51	87
Other comprehensive income (loss)	17	19	51	87
Comprehensive income	635	641	1,827	1,493
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	622	615	1,770	1,415
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(68)	96	173	(177)
Change in derivatives designated as cash flow hedges	2	1	8	36
Change in pension and post-retirement defined benefit plans	19	27	58	82
Other comprehensive income before income taxes	(47)	124	239	(59)
Income tax recovery (expense) on above items	3	(22)	(41)	(10)
Equity accounted investments	61	(83)	(147)	156
Other comprehensive income (loss)	17	19	51	87
Comprehensive income	639	634	1,821	1,502
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	186	200	568	552
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	60	(84)	(150)	153
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	1	1	3	4
Other comprehensive income before income taxes	61	(83)	(147)	157
Income tax recovery (expense) on above items	0	0	0	(1)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	61	(83)	(147)	156
Comprehensive income	$ 247	$ 117	$ 421	$ 708