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Employee Benefit Plans (Amounts to be Amortized in the Next Fiscal Year) (Details) CAD in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 CAD
Pension Plan [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Defined Benefit Plan, Future Amortization of Gain (Loss) | CAD (53)
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit) | 1
Regulated assets | (16)
Total | (68)
Non-pension Benefit Plans [Member |
Defined Benefit Plan Disclosure [Line Items] |
Defined Benefit Plan, Future Amortization of Gain (Loss) | (1)
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit) | 8
Regulated assets | 3
Total | CAD 10

X
- Definition Amount included in accumulated other comprehensive income (AOCI) related to Regulated assets expected to be recognized as components of net periodic benefit cost (credit) for the fiscal year that follows the most recent annual statement of financial position. + 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 included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation). + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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Period Type: | duration

X
- Definition Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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Balance Type: | debit
Period Type: | duration

X
- Details
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X
- Details
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