Condensed Consolidating Financial Information - Interim Condensed Consolidating Statements of Comprehensive Income (Details) - CAD CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Nonoperating Income (Expense)	CAD 9	CAD 5	CAD 190	CAD (68)
Net income	328	390	868	710
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	3	7	40	(30)
Change in derivatives designated as cash flow hedges	(29)	36	(76)	(33)
Change in pension and post-retirement defined benefit plans	43	66	90	138
Other comprehensive income before income taxes	17	109	54	75
Income tax expense on above items	(7)	(35)	(48)	11
Equity accounted investments	0	0	0	0
Other comprehensive (loss) income	10	74	6	86
Comprehensive income	338	464	874	796
Consolidating Adjustments and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Nonoperating Income (Expense)	0	0	0	0
Net income	(449)	(509)	(1,020)	(1,024)
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	7	(44)	282	(356)
Other comprehensive (loss) income	7	(44)	282	(356)
Comprehensive income	(442)	(553)	(738)	(1,380)
CPRL (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Nonoperating Income (Expense)	4	3	73	(15)
Net income	328	390	868	710
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	10	74	6	86
Other comprehensive (loss) income	10	74	6	86
Comprehensive income	338	464	874	796
CPRC (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Nonoperating Income (Expense)	12	8	150	(78)
Net income	328	389	807	723
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	20	59	330	(298)
Change in derivatives designated as cash flow hedges	(29)	36	(76)	(33)
Change in pension and post-retirement defined benefit plans	41	64	86	134
Other comprehensive income before income taxes	32	159	340	(197)
Income tax expense on above items	(5)	(55)	(46)	13
Equity accounted investments	(17)	(30)	(288)	270
Other comprehensive (loss) income	10	74	6	86
Comprehensive income	338	463	813	809
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Nonoperating Income (Expense)	(7)	(6)	(33)	25
Net income	121	120	213	301
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	(17)	(52)	(290)	268
Change in derivatives designated as cash flow hedges	0	0	0	0
Change in pension and post-retirement defined benefit plans	2	2	4	4
Other comprehensive income before income taxes	(15)	(50)	(286)	272
Income tax expense on above items	(2)	20	(2)	(2)
Equity accounted investments	0	0	0	0
Other comprehensive (loss) income	(17)	(30)	(288)	270
Comprehensive income	CAD 104	CAD 90	CAD (75)	CAD 571