Income taxes (Details 1) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income tax expense reconciliation [Abstract]
Canadian statutory federal tax rate (in hundredths)	15.00%	15.00%	15.00%
Income tax expense at the Canadian statutory federal tax rate	CAD 739	CAD 731	CAD 654
Income tax expense (recovery) resulting from: [Abstract]
Provincial and foreign taxes	532	550	531
Deferred income tax adjustments due to rate enactments	7	42	0
Gain on disposals	(12)	(11)	(19)
Other	21	24	27
Income tax expense	1,287	1,336	1,193
Cash payments for income taxes	CAD 653	CAD 725	CAD 722

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The portion of the difference, between total income tax expense (benefit) as reported in the Income Statement for the period and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to provincial and foreign federal, state and local income tax expense (benefit).

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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