RETIREMENT BENEFITS - Sensitivities of Certain Key Assumptions (Details) - Pension Plans - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans
Effect of one-percentage-point increase in discount rates	$ 27	$ 35	$ 34
Effect of one-percentage-point decrease in discount rates	(34)	(49)	(52)
Effect of one-percentage-point increase on benefits earned and interest cost for U.S. postretirement plans	(123)	(124)	(123)
Effect of one-percentage-point decrease on benefits earned and interest cost for U.S. postretirement plans	123	124	123
Non-U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans
Effect of one-percentage-point increase in discount rates	(5)	(4)	(16)
Effect of one-percentage-point decrease in discount rates	15	25	25
Effect of one-percentage-point increase on benefits earned and interest cost for U.S. postretirement plans	(60)	(70)	(66)
Effect of one-percentage-point decrease on benefits earned and interest cost for U.S. postretirement plans	$ 60	$ 70	$ 66

The effect of a one-percentage-point decrease in the discount rates on pension expenses.

No definition available.

Name:	c_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInDiscountRatesOnPensionExpenses
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The effect of a one-percentage-point decrease in the expected rates of return on pension expenses.

+ References

No definition available.

+ Details

Name:	c_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInExpectedRatesOfReturnOnPensionExpenses
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The effect of a one-percentage-point increase in the discount rates on pension expenses.

+ References

No definition available.

+ Details

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

- Definition

The effect of a one-percentage-point increase in the expected rates of return on pension expenses.

+ References

No definition available.

+ Details

Name:	c_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseInExpectedRatesOfReturnOnPensionExpenses
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: