QUARTERLY FINANCIAL DATA (Details) - CAD CAD / shares in Units, CAD in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	CAD 12,889	CAD 9,227	CAD 11,116	CAD 11,146	CAD 9,338	CAD 8,488	CAD 7,939	CAD 8,795	CAD 44,378	CAD 34,560	CAD 33,794
Operating income/(loss)	(2,961)	1,490	1,684	1,358	329	(216)	794	1,674	1,571	2,581	1,862
Earnings	65	1,015	1,241	945	847	(237)	352	1,347	3,266	2,309	(159)
Earnings attributable to controlling interests	291	847	1,000	721	441	(30)	372	1,286	2,859	2,069	251
Earnings/(loss) attributable to common shareholders	CAD 207	CAD 765	CAD 919	CAD 638	CAD 365	CAD (103)	CAD 301	CAD 1,213	CAD 2,529	CAD 1,776	CAD (37)
Earnings per common share
Basic (in dollars per share)	CAD 0.13	CAD 0.47	CAD 0.56	CAD 0.54	CAD 0.39	CAD (0.11)	CAD 0.33	CAD 1.38	CAD 1.66	CAD 1.95	CAD (0.04)
Diluted (in dollars per share)	CAD 0.12	CAD 0.47	CAD 0.56	CAD 0.54	CAD 0.39	CAD (0.11)	CAD 0.33	CAD 1.38	CAD 1.65	CAD 1.93	CAD (0.04)

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Amount after tax of income (loss) from continuing operations including portion attributable to the noncontrolling interest.

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The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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