Property, Plant And Equipment - Schedule of Jointly-Owned Utility Plants (Details) $ in Millions	Dec. 31, 2024 CAD ($)
Jointly Owned Facilities [Line Items]
Cost	$ 3,126
Accumulated Depreciation	(1,191)
Net Book Value	1,935
Transmission Facilities
Jointly Owned Facilities [Line Items]
Cost	1,704
Accumulated Depreciation	(489)
Net Book Value	$ 1,215
Springerville Common Facilities
Jointly Owned Facilities [Line Items]
Ownership (percent)	86.00%
Cost	$ 580
Accumulated Depreciation	(344)
Net Book Value	$ 236
Springerville Coal Handling Facilities
Jointly Owned Facilities [Line Items]
Ownership (percent)	83.00%
Cost	$ 299
Accumulated Depreciation	(154)
Net Book Value	$ 145
Four Corners Units 4 and 5 ("Four Corners")
Jointly Owned Facilities [Line Items]
Ownership (percent)	7.00%
Cost	$ 311
Accumulated Depreciation	(155)
Net Book Value	$ 156
Gila River Common Facilities
Jointly Owned Facilities [Line Items]
Ownership (percent)	50.00%
Cost	$ 131
Accumulated Depreciation	(52)
Net Book Value	$ 79
Luna Energy Facility ("Luna")
Jointly Owned Facilities [Line Items]
Ownership (percent)	33.30%
Cost	$ 101
Net Book Value	104
Luna Energy Facility ("Luna") \| Adjustment
Jointly Owned Facilities [Line Items]
Accumulated Depreciation	$ 3

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479070/980-360-S99-1

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_JointlyOwnedUtilityPlantInterestsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total period end amount of plant in service and construction in progress net of accumulated depreciation for the utility's share of jointly owned electricity generation plant.

+ References

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantNetOwnershipAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

+ Details

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

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=us-gaap_JointlyOwnedElectricityTransmissionAndDistributionSystemMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=fts_SpringervilleCommonFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=fts_JointlyOwnedElectricityGenerationPlantSpringervilleCoalHandlingFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=fts_JointlyOwnedElectricityGenerationPlantFourCornersUnits4and5Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=fts_JointlyOwnedElectricityGenerationPlantGilaRiverCommonFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=fts_JointlyOwnedElectricityGenerationPlantLunaEnergyFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	fts_NettingAxis=fts_NettingAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: