Income Taxes (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
INCOME TAXES.
Current year	CAD 1,150.0	CAD 222.0
Adjustments to current income tax of prior years	59.0	(69.0)
Origination of temporary differences	425.0	(313.0)
Adjustments in respect of deferred income tax of prior years	(70.0)	67.0
Changes in tax rates and legislation	(106.0)	(190.0)
Recognition of previously unrecognized deferred tax assets		(76.0)
Total tax expense (income)	CAD 1,458.0	CAD (359.0)

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 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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