Long Term Debt (Revolving credit facilities, outstanding borrowings and available capacity) (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Available capacity under existing agreements	$ 2,677	$ 2,463
Letters of credit issued inside credit facilities	4	3
Use of available facilities	1,628	1,528
Available capacity under existing agreements	1,049	935
Advances on the revolving credit facility	1,624	1,525
NSPI
Debt Instrument [Line Items]
Letters of credit issued inside credit facilities	63	52
Revolving credit facility
Debt Instrument [Line Items]
Available capacity under existing agreements	1,528	1,629
Borrowings under credit facilities	569	771
Letters of credit issued inside credit facilities	31	65
Use of available facilities	600	836
Available capacity under existing agreements	928	793
Advances on the revolving credit facility	50
Revolving credit facility \| Emera
Debt Instrument [Line Items]
Available capacity under existing agreements	$ 900	900
Maturity	Jun. 30, 2024
Revolving credit facility \| NSPI
Debt Instrument [Line Items]
Available capacity under existing agreements	$ 600	600
Maturity	Oct. 31, 2024
Revolving credit facility \| Emera Maine
Debt Instrument [Line Items]
Available capacity under existing agreements	$ 0	104
Revolving credit facility \| ECI
Debt Instrument [Line Items]
Available capacity under existing agreements	$ 28	$ 25
Revolving credit facility \| Minimum \| ECI
Debt Instrument [Line Items]
Maturity	Dec. 31, 2021
Revolving credit facility \| Maximum \| ECI
Debt Instrument [Line Items]
Maturity	Dec. 31, 2023

Advances against the line of credit facility which can be made by way of overdraft.

No definition available.

Name:	ema_CreditFacilityAdvances
Namespace Prefix:	ema_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowed funds under the facility.

+ References

No definition available.

+ Details

Name:	ema_UseOfAvailableFacilities
Namespace Prefix:	ema_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_ConsolidatedEntitiesAxis=ema_NovaScotiaPowerIncMember
Namespace Prefix:
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- Details

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Namespace Prefix:
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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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- Details

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