Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 480	CAD 328	CAD 911	CAD 868
Net gain in foreign currency translation adjustments, net of hedging activities	14	3	19	40
Change in derivatives designated as cash flow hedges	4	(29)	9	(76)
Change in pension and post-retirement defined benefit plans	37	43	75	90
Other comprehensive income before income taxes	55	17	103	54
Income tax expense on above items	(26)	(7)	(44)	(48)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	29	10	59	6
Comprehensive income	509	338	970	874
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(591)	(449)	(1,157)	(1,020)
Net 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 expense on above items	0	0	0	0
Equity accounted investments	73	7	82	282
Other comprehensive income (loss)	73	7	82	282
Comprehensive income	(518)	(442)	(1,075)	(738)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	480	328	911	868
Net 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 expense on above items	0	0	0	0
Equity accounted investments	29	10	59	6
Other comprehensive income (loss)	29	10	59	6
Comprehensive income	509	338	970	874
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	467	328	881	807
Net gain in foreign currency translation adjustments, net of hedging activities	117	20	162	330
Change in derivatives designated as cash flow hedges	4	(29)	9	(76)
Change in pension and post-retirement defined benefit plans	36	41	72	86
Other comprehensive income before income taxes	157	32	243	340
Income tax expense on above items	(26)	(5)	(43)	(46)
Equity accounted investments	(102)	(17)	(141)	(288)
Other comprehensive income (loss)	29	10	59	6
Comprehensive income	496	338	940	813
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	124	121	276	213
Net gain in foreign currency translation adjustments, net of hedging activities	(103)	(17)	(143)	(290)
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	1	2	3	4
Other comprehensive income before income taxes	(102)	(15)	(140)	(286)
Income tax expense on above items	0	(2)	(1)	(2)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	(102)	(17)	(141)	(288)
Comprehensive income	CAD 22	CAD 104	CAD 135	CAD (75)