SHARE-BASED COMPENSATION (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
2020 FORTIS RESTRICTED STOCK UNIT PLAN
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, valuation, share equivalent, number (in shares)	1
Allocated share of probable payout	$ 2	$ 1
Allocated share-based compensation expense	$ 0	$ 1
2020 FORTIS RESTRICTED STOCK UNIT PLAN \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awarded during the period (in shares)	20,794	15,751
2015 Share Unit Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, valuation, share equivalent, number (in shares)	1
Allocated share of probable payout	$ 9	$ 10
Allocated share-based compensation expense	$ 4	$ 3	$ 4
2015 Share Unit Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awarded during the period (in shares)	2,401	1,918	33,489
2015 Share Unit Plan \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awarded during the period (in shares)	44,931	35,328	66,978

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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-Publisher FASB
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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements payable after one year (or the normal operating cycle, if longer). Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

+ References

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- 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.

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- Definition

Number of shares issued under share-based payment arrangement.

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