DEBT - Trust Preferred Securities (Details) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2014
Trust Preferred Securities
Liquidation value	$ 2,596
Junior subordinated debentures owned by the Trust, amount	2,602
Citigroup Capital III
Trust Preferred Securities
Securities issued (in shares)	194,053
Liquidation value	194
Coupon rate (as a percent)	7.625%
Common shares issued to parent (in shares)	6,003
Junior subordinated debentures owned by the Trust, amount	200
Citigroup Capital XIII
Trust Preferred Securities
Securities issued (in shares)	89,840,000
Liquidation value	2,246
Coupon rate (as a percent)	7.875%
Common shares issued to parent (in shares)	1,000
Junior subordinated debentures owned by the Trust, amount	2,246
Citigroup Capital XVIII
Trust Preferred Securities
Securities issued (in shares)	99,901
Liquidation value	156
Coupon rate (as a percent)	6.829%
Common shares issued to parent (in shares)	50
Junior subordinated debentures owned by the Trust, amount	$ 156

This element represents the proceeds received from the trust at the date of issuance of the junior subordinated debentures to the trust.

No definition available.

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

This element represents the common shares issued by subsidiary trust to parent.

No definition available.

Name:	c_SubsidiaryTrustCommonSharesIssuedToParent
Namespace Prefix:	c_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

This element represents the coupon rate of the trust preferred securities.

No definition available.

Name:	c_TrustPreferredSecuritiesCouponRate
Namespace Prefix:	c_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

This element represents the number of trust preferred securities issued as of the balance sheet date.

No definition available.

Name:	c_TrustPreferredSecuritiesIssued
Namespace Prefix:	c_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Name:	c_TrustPreferredSecuritiesLineItems
Namespace Prefix:	c_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the notional value received by investors from the trusts at the time of issuance.

No definition available.

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

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=c_CitigroupCapitalIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=c_CitigroupCapitalXIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=c_CitigroupCapitalXVIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: