Accumulated Other Comprehensive Income (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-regulated fuel for generation and purchased power	CAD 313	CAD 336
Income (Loss) from Equity Method Investments	100	108
Operating, maintenance and general	1,137	666
Other Income (Expense)	174	141
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	244	545
Income tax expense (recovery)	(22)	93
Net income	266	452
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	65	114
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	11	5
Income tax expense (recovery)	0	2
Net income	11	7
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Power and Gas Swaps [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-regulated fuel for generation and purchased power	(2)	(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Equity Method Investments	1	1
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Foreign Exchange Forward [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Regulated	12	9
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	15	115
Income tax expense (recovery)	(3)	(8)
Net income	12	107
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating, maintenance and general	41	50
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating, maintenance and general	(9)	(7)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Defined Benefit Plans Adjustment, Net Transition Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Other Postretirement Benefit Expense	(17)	72
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Available For Sale Securities Gain Loss Including Portion Attributable To Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income (Expense)	(4)	0
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	(4)	0
Income tax expense (recovery)	0	0
Net income	(4)	0
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Equity Method Investment, Realized Gain (Loss) on Disposal	54	0
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	54	0
Income tax expense (recovery)	(8)	0
Net income	CAD 46	CAD 0

The amount of fuel, and purchased power charged against earnings for the period related to non-regulated operations.

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Amount of gain (loss) on sale or disposal of an equity method investment.

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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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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of income (expense) related to nonoperating activities, classified as other.

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The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

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- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The total amount of regulated operating revenues recognized during the period.

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- Definition

The amount of operating expenses for the period that are associated with the utility's normal revenue producing operation; including selling, general, and administrative expenses, costs incurred for routine plant repairs and maintenance, and operations.

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