Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 510	CAD 347	CAD 1,421	CAD 1,215
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	19	(7)	38	33
Change in derivatives designated as cash flow hedges	2	1	11	(75)
Change in pension and post-retirement defined benefit plans	38	47	113	137
Other comprehensive income before income taxes	59	41	162	95
Income tax expense on above items	(34)	(3)	(78)	(51)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	25	38	84	44
Comprehensive income (loss)	535	385	1,505	1,259
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(641)	(512)	(1,798)	(1,532)
Net gain (loss) 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	134	(103)	216	179
Other comprehensive income (loss)	134	(103)	216	179
Comprehensive income (loss)	(507)	(615)	(1,582)	(1,353)
CPRL (Parent Guarantor) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	510	347	1,421	1,215
Net gain (loss) 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	25	38	84	44
Other comprehensive income (loss)	25	38	84	44
Comprehensive income (loss)	535	385	1,505	1,259
CPRC (Subsidiary Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	505	359	1,386	1,166
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	180	(70)	342	260
Change in derivatives designated as cash flow hedges	2	1	11	(75)
Change in pension and post-retirement defined benefit plans	36	45	108	131
Other comprehensive income before income taxes	218	(24)	461	316
Income tax expense on above items	(34)	(3)	(77)	(49)
Equity accounted investments	(159)	65	(300)	(223)
Other comprehensive income (loss)	25	38	84	44
Comprehensive income (loss)	530	397	1,470	1,210
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	136	153	412	366
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	(161)	63	(304)	(227)
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	2	2	5	6
Other comprehensive income before income taxes	(159)	65	(299)	(221)
Income tax expense on above items	0	0	(1)	(2)
Equity accounted investments	0	0	0	0
Other comprehensive income (loss)	(159)	65	(300)	(223)
Comprehensive income (loss)	CAD (23)	CAD 218	CAD 112	CAD 143