Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	CAD 347	CAD 323	CAD 1,215	CAD 1,033
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(7)	(33)	33	(63)
Change in derivatives designated as cash flow hedges	1	(45)	(75)	(78)
Change in pension and post-retirement defined benefit plans	47	65	137	203
Other comprehensive income (loss) before income taxes	41	(13)	95	62
Income tax expense on above items	(3)	33	(51)	44
Equity accounted investments	0	0	0	0
Other comprehensive (loss) income	38	20	44	106
Comprehensive income	385	343	1,259	1,139
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	(512)	(597)	(1,532)	(1,621)
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 (loss) before income taxes	0	0	0	0
Income tax expense on above items	0	0	0	0
Equity accounted investments	(103)	(279)	179	(635)
Other comprehensive (loss) income	(103)	(279)	179	(635)
Comprehensive income	(615)	(876)	(1,353)	(2,256)
CPRL (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	347	323	1,215	1,033
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 (loss) before income taxes	0	0	0	0
Income tax expense on above items	0	0	0	0
Equity accounted investments	38	20	44	106
Other comprehensive (loss) income	38	20	44	106
Comprehensive income	385	343	1,259	1,139
CPRC (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	359	345	1,166	1,068
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(70)	(291)	260	(589)
Change in derivatives designated as cash flow hedges	1	(45)	(75)	(78)
Change in pension and post-retirement defined benefit plans	45	64	131	198
Other comprehensive income (loss) before income taxes	(24)	(272)	316	(469)
Income tax expense on above items	(3)	33	(49)	46
Equity accounted investments	65	259	(223)	529
Other comprehensive (loss) income	38	20	44	106
Comprehensive income	397	365	1,210	1,174
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	153	252	366	553
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	63	258	(227)	526
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	2	1	6	5
Other comprehensive income (loss) before income taxes	65	259	(221)	531
Income tax expense on above items	0	0	(2)	(2)
Equity accounted investments	0	0	0	0
Other comprehensive (loss) income	65	259	(223)	529
Comprehensive income	CAD 218	CAD 511	CAD 143	CAD 1,082