Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

+ Details

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

- Definition

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477657/942-210-S45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478478/942-210-S50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

Investments - Consolidated Investments (Details) - USD ($) $ in Millions	Sep. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Available-for-sale securities
Amortized Cost	$ 55,495		$ 55,292
Allowance for Expected Credit Losses	(71)	$ (71)	(104)	$ (96)	$ (97)	$ (62)
Gross Unrealized Gains	180		603
Gross Unrealized Losses	(4,892)		(3,091)
Fair Value	50,712		52,700
Asset-backed securities
Available-for-sale securities
Amortized Cost	18,128		18,847
Allowance for Expected Credit Losses	(12)	(14)	(25)	(21)	(24)	(13)
Gross Unrealized Gains	123		166
Gross Unrealized Losses	(390)		(256)
Fair Value	17,849		18,732
Commercial mortgage-backed securities
Available-for-sale securities
Amortized Cost	4,340		5,298
Allowance for Expected Credit Losses	(57)	(56)	(61)	(55)	(53)	(49)
Gross Unrealized Gains	9		57
Gross Unrealized Losses	(186)		(139)
Fair Value	4,106		5,155
Corporates
Available-for-sale securities
Amortized Cost	26,649		25,333
Allowance for Expected Credit Losses	0		(17)	(19)	(20)	0
Gross Unrealized Gains	27		290
Gross Unrealized Losses	(3,729)		(2,356)
Fair Value	22,947		23,250
Hybrids
Available-for-sale securities
Amortized Cost	636		625
Allowance for Expected Credit Losses	0		0
Gross Unrealized Gains	3		6
Gross Unrealized Losses	(40)		(22)
Fair Value	599		609
Municipals
Available-for-sale securities
Amortized Cost	1,532		1,562
Allowance for Expected Credit Losses	0		0
Gross Unrealized Gains	1		4
Gross Unrealized Losses	(309)		(211)
Fair Value	1,224		1,355
Residential mortgage-backed securities
Available-for-sale securities
Amortized Cost	3,513		2,840
Allowance for Expected Credit Losses	(2)	$ (1)	(1)	$ (1)	$ 0	$ 0
Gross Unrealized Gains	17		76
Gross Unrealized Losses	(168)		(70)
Fair Value	3,360		2,845
U.S. Government
Available-for-sale securities
Amortized Cost	392		495
Allowance for Expected Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(11)		(2)
Fair Value	381		493
Foreign Governments
Available-for-sale securities
Amortized Cost	305		292
Allowance for Expected Credit Losses	0		0
Gross Unrealized Gains	0		4
Gross Unrealized Losses	(59)		(35)
Fair Value	$ 246		$ 261