Fair Value Measurements - Schedule of financial assets and liabilities carried at fair value (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other comprehensive income attributable to redeemable non-controlling interest	$ 10	$ (26)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	(411)	(231)
Included in earnings	(186)	(64)
Included in other comprehensive income	5	(4)
Net loss attributable to redeemable non-controlling interest	0	0
Other comprehensive income attributable to redeemable non-controlling interest	0	0
Adjustment of redeemable non-controlling interest to redemption at fair value	0	0
Ending balance	(592)	(299)
Change in unrealized gains or losses for the period included in earnings	(186)	(64)
Change in unrealized gains or losses for the period included in other comprehensive income	4	(6)
Fair Value, Inputs, Level 3 [Member] \| Contingentent Consideration [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	(20)	(22)
Included in earnings	0	0
Included in other comprehensive income	1	2
Net loss attributable to redeemable non-controlling interest	0	0
Other comprehensive income attributable to redeemable non-controlling interest	0	0
Adjustment of redeemable non-controlling interest to redemption at fair value	0	0
Ending balance	(19)	(20)
Change in unrealized gains or losses for the period included in earnings	0	0
Change in unrealized gains or losses for the period included in other comprehensive income	0	0
Fair Value, Inputs, Level 3 [Member] \| Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	9	11
Included in earnings	(2)	0
Included in other comprehensive income	0	0
Net loss attributable to redeemable non-controlling interest	0	0
Other comprehensive income attributable to redeemable non-controlling interest	0	0
Adjustment of redeemable non-controlling interest to redemption at fair value	0	0
Ending balance	7	11
Change in unrealized gains or losses for the period included in earnings	(2)	0
Change in unrealized gains or losses for the period included in other comprehensive income	0	0
Fair Value, Inputs, Level 3 [Member] \| Fox Option liability [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	(400)	(220)
Included in earnings	(184)	(64)
Included in other comprehensive income	4	(6)
Net loss attributable to redeemable non-controlling interest	0	0
Other comprehensive income attributable to redeemable non-controlling interest	0	0
Adjustment of redeemable non-controlling interest to redemption at fair value	0	0
Ending balance	(580)	(290)
Change in unrealized gains or losses for the period included in earnings	(184)	(64)
Change in unrealized gains or losses for the period included in other comprehensive income	4	(6)
Fair Value, Inputs, Level 3 [Member] \| Redeemable non- controlling interest at fair value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Redeemable non- controlling interest at fair value, Beginning balance	(1,100)	(781)
Included in earnings	0	0
Included in other comprehensive income	0	0
Net loss attributable to redeemable non-controlling interest	1	4
Other comprehensive income attributable to redeemable non-controlling interest	11	(17)
Adjustment of redeemable non-controlling interest to redemption at fair value	(216)	(125)
Redeemable non- controlling interest at fair value, Ending balance	(1,304)	(919)
Change in unrealized gains or losses for the period included in earnings	0	0
Change in unrealized gains or losses for the period included in other comprehensive income	$ 0	$ 0

Adjustment of redeemable non-controlling interest to redemption at fair value.

No definition available.

Name:	flut_AdjustmentOfRedeemableNoncontrollingInterestToRedemptionAtFairValue
Namespace Prefix:	flut_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Movements in respect of the financial assets and liabilities carried at fair value.

+ References

No definition available.

+ Details

Name:	flut_MovementsInRespectOfTheFinancialAssetsAndLiabilitiesCarriedAtFairValue
Namespace Prefix:	flut_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrealized gain (loss) recognized in income from asset (liability) measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_FairValueAssetLiabilityRecurringBasisStillHeldUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in income from asset and liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

- Definition

Amount of unrealized gain (loss) recognized in other comprehensive income (OCI) from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value using unobservable input (level 3) and still held.

+ References

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityRecurringBasisStillHeldUnrealizedGainLossOci
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset (liability) measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetLiabilityGainLossOci
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of Net Income (Loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(17))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4J
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481175/810-10-55-4J

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

+ Details

Name:	us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after tax of other comprehensive income (loss) attributable to noncontrolling interests.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 19
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481231/810-10-45-19

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 20
-SubTopic 10
-Topic 810
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481231/810-10-45-20

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-SubTopic 10
-Topic 810
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1A

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Redemption value, as if currently redeemable, of redeemable noncontrolling interest classified as temporary equity and the election has been made to accrete changes in redemption value to the earliest redemption date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 3A
-Subparagraph 24(b)
-SubTopic 10
-Topic 480
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

+ Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=flut_ContingententConsiderationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_FairValueOptionOtherEligibleItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=flut_RedeemableNonControllingInterestAtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: