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INCOME TAXES - Schedule of Provision For Income Tax Reconciliation (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Canadian statutory income tax rate	27.00%	27.00%	26.00%
Income tax provision at statutory rate	$ 776	$ (287)	$ (173)
UK PRT and other taxes	(67)	(324)	(232)
Impact of deductible UK PRT and other taxes on corporate income tax	28	131	119
Foreign and domestic tax rate differentials	(43)	(54)	(157)
Non-taxable portion of capital gains/losses	(86)	(80)	36
Stock options exercised for common shares	33	94	(12)
Income tax rate and other legislative changes	10	(107)	362
Non-taxable gain on corporate acquisitions	(63)	0	0
Revisions arising from prior year tax filings	(3)	(120)	32
Change in unrecognized capital loss carryforward asset	(86)	(80)	36
Other	(23)	(32)	(41)
Income tax expense (recovery)	$ 476	$ (859)	$ (30)

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Tax Effect From Deferred Tax Not Recognized

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The applicable income tax rate.

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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 that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that the entity does not separately disclose in the same statement or note. [Refer: Accounting profit; Applicable tax rate]

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to changes in the tax rate. [Refer: Accounting profit]

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