Line Of Credit Facility, Additional Borrowing Capacity, Expansion

No definition available.

Name:	fts_LineOfCreditFacilityAdditionalBorrowingCapacityExpansion
Namespace Prefix:	fts_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt 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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

Name:	us-gaap_ExtinguishmentOfDebtAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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_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

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

Long-Term Debt - Narrative (Details) $ in Millions, $ in Millions	1 Months Ended				6 Months Ended
	Jul. 31, 2020 USD ($)	May 31, 2020 USD ($)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 CAD ($)	Jun. 30, 2020 CAD ($)	Jul. 31, 2020 CAD ($)	Apr. 30, 2020 CAD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2019 CAD ($)
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 5,863				$ 5,590
Credit facilities unused					$ 4,793				$ 4,324
No one bank \| Bank concentration risk \| Credit facility
Debt Instrument [Line Items]
Concentration risk percentage					25.00%
Caribbean Utilities \| Unsecured Revolving Committed Credit Facility
Debt Instrument [Line Items]
Increase in unsecured debt								$ 20
FortisBC Energy \| Uncommitted Letter Of Credit Facility
Debt Instrument [Line Items]
Debt instrument, term				2 years
Maximum borrowing capacity				$ 55
FortisAlberta \| Non-Revolving Committed Facility
Debt Instrument [Line Items]
Debt instrument, term				1 year
Maximum borrowing capacity				$ 150
Corporate \| Unsecured Revolving Term Committed Facility
Debt Instrument [Line Items]
Debt instrument, term			1 year
Maximum borrowing capacity							$ 500
Three Point One Three Percent First Mortgage Bonds \| ITC \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, term	31 years
Debt instrument, face amount	$ 180
Interest rate	3.13%					3.13%
Three Point Six Two Percent Unsecured Senior Notes \| Central Hudson \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, term	40 years
Debt instrument, face amount	$ 30
Interest rate	3.62%					3.62%
Two Point Five Four Percent Unsecured Debentures \| FortisBC Energy \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, term	30 years
Debt instrument, face amount						$ 200
Interest rate	2.54%					2.54%
Committed facilities with maturities ranging from 2021 through 2025
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 5,600
Unsecured Non-Revolving Uncommitted Credit Facility \| UNS Energy
Debt Instrument [Line Items]
Termination of debt			$ 225
Uncommitted Credit Facility \| Central Hudson
Debt Instrument [Line Items]
Termination of debt		$ 10
Unsecured Revolving Committed Credit Facility \| Central Hudson \| Subsequent Event
Debt Instrument [Line Items]
Termination of debt	$ 50