INCOME TAXES - Reconciliation of Expense (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income/(Loss) before income taxes	CAD 922	CAD (1,105)	CAD 2,824
Federal and provincial statutory tax rate (percent)	27.00%	26.00%	25.00%
Expected income tax expense/(recovery)	CAD 249	CAD (287)	CAD 706
Income tax differential related to regulated operations	81	159	129
Foreign tax rate differentials	(196)	14	25
Income from equity investments and non-controlling interests	(68)	(56)	(38)
Asset impairment charges	242	170	0
Non-deductible amounts	18	0	0
Tax rate and legislative changes		34
Other	23	1	8
Total Income Tax Expense/(Recovery)	349	35	CAD 830
Foreign tax rate differential related to asset impairments, amount	CAD 112	CAD 311

Effective Income Tax Rate Reconciliation Amount, Foreign Tax Rate Differential Related To Asset Impairments, Amount

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The portion of the difference between total income tax expense (benefit) as reported in the income statement for the year/accounting 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 income from equity investments and non-controlling interests.

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

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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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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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 foreign income tax expense (benefit).

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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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