Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net income	$ 409	$ 434
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(65)	16
Change in derivatives designated as cash flow hedges	2	2
Change in pension and post-retirement defined benefit plans	45	20
Other comprehensive (loss) income before income taxes	(18)	38
Income tax recovery (expense) on above items	60	(22)
Equity accounted investments	0	0
Other comprehensive income (loss)	42	16
Comprehensive income	451	450
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(632)	(552)
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	0	0
Change in derivatives designated as cash flow hedges	0	0
Change in pension and post-retirement defined benefit plans	0	0
Other comprehensive (loss) income before income taxes	0	0
Income tax recovery (expense) on above items	0	0
Equity accounted investments	(533)	87
Other comprehensive income (loss)	(533)	87
Comprehensive income	(1,165)	(465)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	409	434
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	0	0
Change in derivatives designated as cash flow hedges	0	0
Change in pension and post-retirement defined benefit plans	0	0
Other comprehensive (loss) income before income taxes	0	0
Income tax recovery (expense) on above items	0	0
Equity accounted investments	42	16
Other comprehensive income (loss)	42	16
Comprehensive income	451	450
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	430	428
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(555)	120
Change in derivatives designated as cash flow hedges	2	2
Change in pension and post-retirement defined benefit plans	44	19
Other comprehensive (loss) income before income taxes	(509)	141
Income tax recovery (expense) on above items	60	(22)
Equity accounted investments	491	(103)
Other comprehensive income (loss)	42	16
Comprehensive income	472	444
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	202	124
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	490	(104)
Change in derivatives designated as cash flow hedges	0	0
Change in pension and post-retirement defined benefit plans	1	1
Other comprehensive (loss) income before income taxes	491	(103)
Income tax recovery (expense) on above items	0	0
Equity accounted investments	0	0
Other comprehensive income (loss)	491	(103)
Comprehensive income	$ 693	$ 21