CONSOLIDATED STATEMENTS OF INCOME - CAD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 2,006	$ 1,898	$ 1,750	$ 1,662	$ 1,713	$ 1,595	$ 1,643	$ 1,603	$ 7,316	$ 6,554	$ 6,232
Operating expenses
Compensation and benefits									1,468	1,309	1,356
Fuel									918	677	567
Materials									201	190	180
Equipment rents									130	142	173
Depreciation and amortization									696	661	640
Purchased services and other									1,072	1,056	905
Total operating expenses									4,485	4,035	3,821
Operating income	874	790	627	540	682	622	611	604	2,831	2,519	2,411
Less:
Other expense (income)									174	(178)	(45)
Other components of net periodic benefit recovery									(384)	(274)	(167)
Net interest expense									453	473	471
Income before income tax expense									2,588	2,498	2,152
Income tax expense									637	93	553
Net income	$ 545	$ 622	$ 436	$ 348	$ 984	$ 510	$ 480	$ 431	$ 1,951	$ 2,405	$ 1,599
Earnings per share
Basic earnings per share	$ 3.84	$ 4.36	$ 3.05	$ 2.41	$ 6.79	$ 3.50	$ 3.28	$ 2.94	$ 13.65	$ 16.49	$ 10.69
Diluted earnings per share	$ 3.83	$ 4.35	$ 3.04	$ 2.41	$ 6.77	$ 3.50	$ 3.27	$ 2.93	$ 13.61	$ 16.44	$ 10.63
Weighted-average number of shares (millions)
Basic									142.9	145.9	149.6
Diluted									143.3	146.3	150.5
Freight [Member]
Revenues
Revenues									$ 7,152	$ 6,375	$ 6,060
Non-freight [Member]
Revenues
Revenues									$ 164	$ 179	$ 172