GOODWILL AND INTANGIBLE ASSETS - Components of Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	$ 10,488	$ 10,454
Accumulated amortization of Intangible assets (excluding MSRs)	6,849	6,720
Net carrying amount of Intangible assets (excluding MSRs)	3,639	3,734
Gross carrying amount, Mortgage servicing rights (MSRs)	770	760
Mortgage servicing rights (MSRs)	770	760
Gross carrying amount of Intangible assets	11,258	11,214
Accumulated amortization of Intangible assets	6,849	6,720
Total intangible assets	4,409	4,494
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	218	197
Net carrying amount of Intangible assets (excluding MSRs)	218	197
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	5,315	5,315
Accumulated amortization of Intangible assets (excluding MSRs)	4,573	4,507
Net carrying amount of Intangible assets (excluding MSRs)	742	808
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	4,578	4,586
Accumulated amortization of Intangible assets (excluding MSRs)	1,940	1,905
Net carrying amount of Intangible assets (excluding MSRs)	2,638	2,681
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	342	325
Accumulated amortization of Intangible assets (excluding MSRs)	302	278
Net carrying amount of Intangible assets (excluding MSRs)	40	47
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	35	31
Accumulated amortization of Intangible assets (excluding MSRs)	34	30
Net carrying amount of Intangible assets (excluding MSRs)	$ 1	$ 1

No definition available.

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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

This element represents the accumulated amortization of all intangible assets, excluding goodwill and mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsAccumulatedAmortization
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the gross carrying amounts of all intangible assets, excluding goodwill and mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

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

- 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

This element represents the accumulated amortization of all intangible assets excluding goodwill but including mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRightsAccumulatedAmortization
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the gross carrying amount of intangible assets excluding goodwill but including mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRightsGrossCarryingAmount
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

This element represents the gross carrying amount of mortgage servicing rights (MSRs) as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Details

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- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_PurchasedCreditCardRelationshipsMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_ContractBasedIntangibleAssetsMember
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Data Type:	na
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- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_OtherCustomerRelationshipsMember
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- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_PresentValueOfFutureProfitsMember
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