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Regulatory Assets and Liabilities (FAM Roll Forward) (Details) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 CAD	Dec. 31, 2016 USD ($)	Dec. 31, 2015 CAD	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD
Fuel Adjustment Mechanism [Roll Forward]
Beginning balance	CAD 94
Over Under Recovery Of Current Period Fuel Costs	29		CAD (24)
Recovery From Rebate	12		56
Non Fuel Revenues To Offset Potential Fuel Related Rate Increase	20		45
Regulated fixed cost deferral related to 2015 demand side management	0		(35)
Interest On Fuel Adjustment Mechanism Balance	61		42
Ending balance	80		94
Regulatory Assets, Current	CAD 94		CAD 94	CAD 80	CAD 94
Regulatory Liability, Current				362	112
Regulatory Liability, Noncurrent				1,277	CAD 353
Recovery Stranded Costs | $		$ 21
FAM [Member]
Fuel Adjustment Mechanism [Roll Forward]
Regulatory Liability, Current				32
Regulatory Liability, Noncurrent				CAD 62

X

- References

No definition available.

+ Details

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Namespace Prefix:	ema_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Interest On Fuel Adjustment Mechanism.

+ References

No definition available.

+ Details

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Namespace Prefix:	ema_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of public utility's amended requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

Name:	ema_NonFuelRevenuesToOffsetPotentialFuelRelatedRateIncrease
Namespace Prefix:	ema_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

No definition available.

+ Details

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- Definition

Recovery from (rebate to) customers from adjustments to prior years fuel costs.

+ References

No definition available.

+ Details

Name:	ema_RecoveryFromRebate
Namespace Prefix:	ema_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The periodic expense to reduce the value of the rate deferral asset that is created when utilities under bill customers during periods of rate increases by deferring rate increases. These customers eventually pay higher rates to repay the utility for the rate deferral.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- Definition

Revenue from billings to utility customers to recover what are also referred to as stranded assets or stranded investments. These are assets that formerly regulated utilities with monopolies on local service are allowed to recover during their transition to deregulated suppliers in competitive markets. Essentially, these investments are sunk costs, made by utilities under the old regulated system, which might not be recovered in a truly competitive marketplace. However, since they were valid investments at the time, the utilities are allowed to recover these costs from customers (for example, an investment in electrical generation assets that may not be recouped if customers are now allowed to purchase electricity from another utility).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Balance Type:	debit
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X

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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Balance Type:	credit
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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Period Type:	instant

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- Details

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