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

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

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

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ 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

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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

- References

No definition available.

+ Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=ema_FinanceTermCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=ema_TecoEnergyIncAndTecoFinanceIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=ema_TampaElectricDivisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=ema_NewMexicoGasCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=ema_GrandBahamaPowerCompanyLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Short Term Debt (Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity) (Details) $ in Millions, $ in Millions				12 Months Ended
	Dec. 19, 2019 USD ($)	Dec. 16, 2019 CAD ($)	Mar. 07, 2019 USD ($)	Dec. 31, 2019 CAD ($)	Feb. 06, 2020 USD ($)	Dec. 20, 2019 USD ($)	Jun. 13, 2019 CAD ($)	Dec. 31, 2018 CAD ($)
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Total available capacity				$ 2,463				$ 2,065
Advances under revolving credit and term facilities				1,525				1,186
Letters of credit issued within the credit facilities				3				3
Total advances under available facilities				1,528				1,189
Available capacity under existing agreements				$ 935				876
Parent Company [Member]
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Total available capacity							$ 900
Term credit facility \| TECO Energy/TECO Finance
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity				Dec. 31, 2020
Total available capacity				$ 649				682
Revolving credit facility \| TECO Energy/TECO Finance
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity				Mar. 22, 2022
Total available capacity				$ 520				546
Revolving credit facility \| Tampa Electric Company
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity	Feb. 04, 2021			Mar. 22, 2022
Total available capacity	$ 325			$ 520	$ 300	$ 400		443
Revolving credit facility \| NMGC
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity				Mar. 22, 2022
Total available capacity				$ 162				171
Revolving credit facility \| GBPC
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Total available capacity				$ 17				18
Non-revolving term credit facility
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity		Dec. 15, 2020
Total available capacity		$ 400
Non-revolving term credit facility \| TECO Energy/TECO Finance
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity			Mar. 05, 2020
Total available capacity			$ 500
Non-revolving term credit facility \| Parent Company [Member]
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity				Dec. 31, 2020
Total available capacity				$ 400				0
Accounts receivable revolving credit facility \| Tampa Electric Company
Short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity
Maturity				Dec. 31, 2021
Total available capacity				$ 195				$ 205