Income Taxes - Summary of Provision for Income Taxes (Detail) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Current
Current taxes on profits for the year	CAD 1,014	CAD 551
Adjustments for current taxes of prior periods	(15)	(14)
Total current taxes	999	537
Deferred
Origination and reversal of temporary differences	444	42
Adjustments to deferred taxes of prior periods	23	(2)
Tax losses not recognized (recognition of previously unrecognized losses)	(9)	(10)
Effect due to tax legislative changes	(19)	20
Total deferred taxes	439	50
Provision for income taxes	CAD 1,438	CAD 587

Adjustments of tax expense (income) recognised in the period for current tax of prior periods.

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Adjustments of tax expense (income) recognised in the period for the deferred tax of prior periods.

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The amount of income taxes payable (recoverable) in respect of the taxable profit (tax loss) for a period.

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The amount of current tax expense (income) and adjustments for the current tax of prior periods. [Refer: Current tax expense (income); Adjustments for current tax of prior periods]

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The amount of tax expense (income) relating to changes in deferred tax liabilities and deferred tax assets. [Refer: Deferred tax assets; Deferred tax liabilities]

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The amount of deferred tax expense or income relating to the creation or reversal of temporary differences. [Refer: Temporary differences [member]; Deferred tax expense (income)]

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The amount of deferred tax expense or income relating to tax rate changes or the imposition of new taxes. [Refer: Deferred tax expense (income)]

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The aggregate amount included in the determination of profit (loss) for the period in respect of current tax and deferred tax that relate to continuing operations. [Refer: Continuing operations [member]; Current tax expense (income); Deferred tax expense (income)]

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The amount of benefit arising from a previously unrecognised tax loss, tax credit or temporary difference of a prior period that is used to reduce deferred tax expense. [Refer: Deferred tax expense (income); Temporary differences [member]; Unused tax losses [member]; Unused tax credits [member]]

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