GOODWILL AND INTANGIBLE ASSETS - Changes in Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Finite and Indefinite-lived Intangible Assets
Beginning balance	$ 3,730
Acquisitions/ renewals/ divestitures	427
Amortization	(371)
Impairments	(4)
FX translation and other	(48)
Ending balance	3,734
Mortgage servicing rights (MSRs)	760	$ 691
Total intangible assets	4,494	$ 4,421
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Beginning balance	937
Acquisitions/ renewals/ divestitures	13
Amortization	(142)
Impairments	0
FX translation and other	0
Ending balance	$ 808
Useful life	10 years
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Beginning balance	$ 2,479
Acquisitions/ renewals/ divestitures	414
Amortization	(208)
Impairments	(4)
FX translation and other	0
Ending balance	$ 2,681
Useful life	20 years
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Beginning balance	$ 73
Acquisitions/ renewals/ divestitures	0
Amortization	(21)
Impairments	0
FX translation and other	(5)
Ending balance	47
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Beginning balance	1
Acquisitions/ renewals/ divestitures	0
Amortization	0
Impairments	0
FX translation and other	0
Ending balance	1
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Beginning balance	240
Acquisitions/ renewals/ divestitures	0
Amortization	0
Impairments	0
FX translation and other	(43)
Ending balance	$ 197

No definition available.

Name:	c_FiniteAndIndefiniteLivedIntangibleAssetsRollForward
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- Definition

Sum of the carrying amounts of all intangible assets, excluding goodwill and excluding mortgage servicing rights, as of the balance sheet date, net of accumulated amortization and impairment charges.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRights
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Intangible Assets, Excluding Mortgage Servicing Rights Acquisitions (Divestitures)

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsAcquisitionsDivestitures
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the aggregate amount of amortization of intangible assets excluding mortgage servicing rights (MSRs) during the period.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsAmortizationOfIntangibleAssets
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the aggregate amount of impairment of intangible assets excluding mortgage servicing rights (MSRs) during the period.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsImpairments
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents net changes to the recorded value of intangible assets excluding mortgage servicing rights (MSRs), due to foreign currency translation adjustments and purchase accounting adjustments.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsTranslationAndPurchaseAccountingAdjustments
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the sum of the carrying amounts of all intangible assets excluding goodwill but including mortgage servicing rights, as of the balance sheet date that is net of accumulated amortization and impairment charges.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRights
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of mortgage servicing rights (MSRs) as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_MortgageServicingRightsMSR
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_PresentValueOfFutureProfitsMember
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- Details

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